Search

Recent discovery of new disease-defining molecular alterations and development of novel targeted therapies has dramatically changed the classification and management of uterine mesenchymal neoplasms. This review discusses diagnostic updates in endometrial stromal sarcoma, PEComa, uterine tumor resembling ovarian sex cord tumor (UTROSCT), inflammatory myofibroblastic tumor, NTRK fusion uterine sarcoma, COL1A1-PDGFB fusion sarcoma, and SMARC-deficient uterine sarcoma. Key clinical, morphologic, immunophenotypic, and molecular features are reviewed, with emphasis on common differential diagnoses and pitfalls, and their impact on prognosis or management. Where applicable, the role of novel targeted therapies is discussed. A stepwise approach to uterine mesenchymal neoplasms can achieve a proper diagnosis and guide appropriate clinical management in most cases. Nonetheless, given the rarity of these tumors, their overlapping pathologic features, and rapid evolution in their classification and management, we advocate a low threshold for diagnostic consultation.

AIMS Most vulvar squamous cell carcinomas are human papillomavirus (HPV)-associated or TP53-mutant. A third category of HPV-independent TP53-wild-type lesions is uncommon and not fully understood. Differentiated exophytic vulvar intraepithelial lesion (DEVIL) has been characterised as a precursor of this latter category. The reproducibility of the diagnosis of DEVIL and its distinction from lesions with overlapping morphology has not been studied. Our aim was to establish the interobserver agreement in the diagnosis of DEVIL and its distinction from neoplastic and reactive conditions of the vulva on haematoxylin and eosin evaluation. METHODS AND RESULTS A set of 35 slides was evaluated by eight reviewers (two trainees and six practising gynaecological pathologists). The set included DEVIL, condyloma, established vulvar precursors [high-grade squamous intraepithelial lesion (HSIL) and differentiated vulvar intraepithelial neoplasia (dVIN)] with superimposed acanthosis or verruciform growth, lichen simplex chronicus (LSC), and psoriasis. Kappa (κ) values were calculated. Overall, interobserver agreement was moderate (κ = 0.56), improving to substantial (κ = 0.7) when evaluation was performed by practising pathologists. Agreement was strong for the diagnosis of HSIL (κ = 0.88), and substantial for the diagnosis of DEVIL (κ = 0.61), condyloma (κ = 0.79), and LSC (κ = 0.72). Agreement was moderate for the diagnosis of dVIN (κ = 0.59) and psoriasis (κ = 0.53). Perfect agreement (6/6) among practising pathologists was observed in 43% of cases, and majority agreement (5/6 or 4/6) was observed in 48% of cases. CONCLUSIONS Reproducibility in the diagnosis of verruciform vulvar lesions, including the novel DEVIL, is acceptable overall. Reproducibility is higher for well-known lesions such as HSIL and condyloma than for more challenging diagnoses such as DEVIL, dVIN, and psoriasis. Agreement is higher among practising gynaecological pathologists, suggesting that training and experience improve reproducibility. Our findings support the inclusion of DEVIL as a diagnostic entity in the classification of vulvar squamous lesions.

Mucinous ovarian tumors rarely harbor mural nodules, which have historically been classified as sarcoma-like, anaplastic carcinomatous, or sarcomatous on the basis of predominant morphologic features. The molecular relationship between mural nodules and associated mucinous ovarian tumors remains poorly characterized, as does the molecular pathogenesis of these mural nodules. Thus, we analyzed the morphological, immunohistochemical, and genetic features of 13 mucinous ovarian tumors and associated mural nodule(s). Three harbored sarcoma-like mural nodules and ten contained anaplastic carcinomatous nodules, including 1 tumor with spatially discrete anaplastic carcinomatous and sarcomatous nodules. Twelve of 13 cases showed genetic evidence of clonality between the mural nodule(s) and associated mucinous ovarian tumor, including all three tumors with sarcoma-like morphology. Mural nodules were genetically identical in the five cases in which there were multiple discrete mural nodules that were sequenced separately. MTAP and p53 immunohistochemistry confirmed the distribution of neoplastic cells in a subset of sarcoma-like and anaplastic carcinomatous nodules. No single recurrent genetic alteration was associated with mural nodule development. No recurrent genetic differences were identified between mural nodules with sarcoma-like, anaplastic carcinomatous, and sarcomatous morphology. Of 11 patients with clinical follow-up, three died of disease 3, 8, and 9 months after diagnosis, but no recurrent genetic events were associated with poor outcome. These molecular data suggest that sarcoma-like, anaplastic carcinomatous, and sarcomatous nodules represent a morphologic spectrum of clonal neoplasms arising in mucinous ovarian tumors rather than three discrete biological entities.

Malignant peritoneal mesothelioma historically carried a grim prognosis, but outcomes have improved substantially in recent decades. The prognostic significance of clinical, morphologic, and immunophenotypic features remains ill-defined. This multi-institutional cohort comprises 225 malignant peritoneal mesotheliomas, which were assessed for 21 clinical, morphologic, and immunohistochemical parameters. For epithelioid mesotheliomas, combining nuclear pleomorphism and mitotic index yielded a composite nuclear grade, using a previously standardized grading system. Correlation of clinical, morphologic, and immunohistochemical parameters with overall and disease-free survival was examined by univariate and multivariate analyses. On univariate analysis, longer overall survival was significantly associated with diagnosis after 2000 (P = 0.0001), age

Immunohistochemistry plays an indispensable role in accurate diagnosis of malignant mesothelioma, particularly in morphologically challenging cases and in biopsy and cytology specimens, where tumor architecture is difficult or impossible to evaluate. Application of a targeted panel of mesothelial- and epithelial-specific markers permits correct identification of tumor lineage in the vast majority of cases. An immunopanel including two mesothelial markers (calretinin, CK5/6, WT-1, or D2-40) and two epithelial markers (MOC-31 and claudin-4) offers good sensitivity and specificity, with adjustments as appropriate for the differential diagnosis. Once mesothelial lineage is established, malignancy-specific studies can help verify a diagnosis of malignant mesothelioma. BAP1 loss, CDKN2A homozygous deletion, and MTAP loss are highly specific markers of malignancy in a mesothelial lesion, and they attain acceptable diagnostic sensitivity when applied as a diagnostic panel. Novel markers of malignancy, such as 5-hmC loss and increased EZH2 expression, are promising, but have not yet achieved widespread clinical adoption. Some diagnostic markers also have prognostic significance, and PD-L1 immunohistochemistry may predict tumor response to immunotherapy. Application and interpretation of these immnuomarkers should always be guided by clinical history, radiographic findings, and above all histomorphology.

Ancillary studies facilitate accurate diagnosis of morphologically challenging mesothelial proliferations. The current diagnostic algorithm proceeds from BAP1 immunohistochemistry to CDKN2A fluorescence in situ hybridization. While MTAP immunohistochemistry has recently shown promise as a surrogate for CDKN2A fluorescence in situ hybridization, it has been examined in only a few single-institution studies. Furthermore, there are no published reports on interobserver agreement or interlaboratory reproducibility for MTAP immunohistochemistry. We performed MTAP immunohistochemistry on 20 benign mesothelial lesions and 99 malignant mesotheliomas from five mesothelioma centers in four countries, and each MTAP stain was independently interpreted by four pathologists. CDKN2A fluorescence in situ hybridization data were available for a subset of cases, and a subset of cases was subjected in MTAP immunohistochemistry in multiple laboratories to assess interlaboratory reproducibility. Interobserver agreement in MTAP immunostain interpretation was excellent for all mesothelial lesions (kappa: 0.85) and for malignant mesothelioma cases only (kappa: 0.82). Interlaboratory reproducibility was also excellent (kappa values for paired protocols: 0.77–0.89). MTAP loss by immunohistochemistry was 78% sensitive and 96% specific for CDKN2A homozygous deletion. MTAP immunohistochemistry is a reliable surrogate for CDKN2A fluorescence in situ hybridization in diagnosis of malignant mesothelioma. Interobserver agreement is excellent for interpretation of MTAP staining, and protocols performed in different laboratories yield concordant MTAP staining results. Rare cases with immunohistochemical MTAP loss may retain normal CDKN2A copy number, and the MTAP staining results should be correlated with clinicopathologic findings and other ancillary studies.

The percentage of sarcomatoid component has an impact on prognosis in patients with biphasic malignant pleural mesothelioma. Recent study showed that the transitional pattern similar to sarcomatoid component of malignant mesothelioma has negative prognostic significance. Practice guidelines recommend quantification of sarcomatoid component despite poor diagnostic reproducibility of biphasic mesothelioma among thoracic pathologists. The aim of this study was to determine the interobserver agreement in the quantification of sarcomatoid component, and in the diagnosis of a transitional component in the biphasic malignant mesothelioma. Thirteen experts in thoracic pathology reviewed the representative H&E and cytokeratin whole-slide images of the 54 biphasic mesotheliomas, without knowledge of BAP1 or p16 deletion status, and completed the survey of 25 questions. The overall interobserver agreement in the assessment of the percentage of the sarcomatoid component in 25% increments was good (wK = 0.62). Excellent agreement was present in 14 of 54 cases (26%), and 3 cases were unanimously scored. Excellent agreement was reached for the cases with 0–24% and > 75% of the sarcomatoid component.The most commonly used criteria for the diagnosis of sarcomatoid component were malignant spindle cells, frank sarcomatoid features and high N/C ratio. The overall interobserver agreement for transitional pattern was fair (wK = 0.40). Unanimous opinion about the absence of transitional pattern was observed in only one case. At least 70% agreement regarding the presence of transitional pattern was observed in 12 cases, with the rest of the cases showing a wide range of disagreement. Morphologic characteristics that favor transitional pattern over non-transitional include sheet-like growth of cohesive, plump, elongated epithelioid cells with well-defined cell borders and a tendency to transition into spindle cells. Our study defined precise morphologic criteria that may be used in the differential diagnosis between transitional pattern and other mesothelioma subtypes including sarcomatoid and epithelioid.

Epithelioid leiomyosarcoma of the uterus is rare and poorly understood. Herein, we characterize a large institutional series of epithelioid leiomyosarcomas aiming to define outcome-determinant diagnostic pathologic features. We also retrieved epithelioid smooth muscle tumors of unknown malignant potential and evaluated a consecutive cohort of leiomyomas for epithelioid subtypes. Of a total of 1177 uterine leiomyosarcomas, 81 (7%) were categorized as epithelioid after review. Epithelioid leiomyosarcoma was strictly defined as having round to polygonal cells with visible pink cytoplasm and round to ovoid nuclei in ≥50% of the tumor volume. Average age was 55 years (range: 26 to 81 y). Median tumor size was 11 cm; tumor was >5 cm in 93% of subjects; 47% were stage 1 at presentation. An infiltrative tumor border was observed, grossly and/or microscopically, in 89% of cases; necrosis was noted in 80%, and vascular invasion in 47%. Mitotic count in 2.4 mm2 (totalling 10 high-power fields, each field 0.55 mm in diameter) ranged from 3 to 100 (median: 26). All cases had moderate, severe or highly pleomorphic atypia. All cases had 2 or 3 of the following: necrosis, at least moderate atypia and ≥4 mitoses in 2.4 mm2. Immunohistochemistry revealed frequent expression of smooth muscle markers including SMA (96%), desmin (95%), and caldesmon (81%). HMB45 and Melan-A were negative in 92% and 100% of cases, respectively. Estrogen and progesterone receptors were expressed by 65% and 54% of tumors, respectively. Follow-up information was available in 68 subjects (median: 23 mo, range: 1 to 254); cancer-related death occurred in 63%, and an additional 15% had recurrent or metastatic disease at last follow-up. Disease-specific survival was shorter in epithelioid leiomyosarcoma patients (median: 44 mo; 35% at 5-y) than in a matched cohort of nonepithelioid leiomyosarcoma (median: 55 mo; 46% at 5-y) (P=0.03). Three epithelioid smooth muscle tumors of unknown malignant potential were evaluated, all

Primary peritoneal malignant mesothelioma (MM) can demonstrate morphologic overlap with low-grade and high-grade tubo-ovarian serous neoplasms; it is also biologically and prognostically distinct from benign mesothelial proliferations. Currently, there is no single biomarker that can definitively distinguish these neoplasms. Sex-determining region Y box 6 (SOX6) immunohistochemistry has been recently described to differentiate pleural epithelioid MM from lung adenocarcinoma, but it has not been evaluated in the peritoneum. SOX6 immunohistochemistry was performed on 43 peritoneal epithelioid MM, 7 peritoneal biphasic MM, 5 well-differentiated papillary mesotheliomas, 5 serous borderline tumors, 29 low-grade serous carcinomas (LGSCs), 20 high-grade serous carcinomas (HGSCs), and 25 cases of peritoneal reactive mesothelial hyperplasia. Quantitative SOX6 expression in epithelioid MM (median, 100% of tumor cells) was significantly greater than in LGSC/serous borderline tumor (median, 90%; P=0.004) and HGSC (median, 45%; P=0.0001). However, when SOX6 is expression is defined as ≥10% of tumor cells, there was no significant difference in the rate of SOX6 positivity between epithelioid MM (41/43, 95%), LGSC (28/29, 97%; P=1.0), and HGSC (17/20, 85%; P=0.16). Quantitative extent of SOX6 expression in epithelioid MM was significantly greater than in biphasic MM (median, 0%; P=0.0001), well-differentiated papillary mesothelioma (median, 20%; P=0.001), and reactive mesothelial hyperplasia (median, 20%; P=0.0001), but not significantly different from flat quiescent mesothelium (median, 90%; P=0.82). SOX6 immunohistochemistry is 95% sensitive for peritoneal epithelioid MM, but is also consistently expressed in LGSC and HGSC, negating its usefulness in this common differential diagnosis. SOX6 also shows variable expression across the spectrum of reactive, benign neoplastic, and malignant mesothelial lesions of the peritoneum, and does not appear to be diagnostically useful in distinguishing benign from malignant mesothelial proliferations.

Accurate distinction of benign mesothelial proliferations from malignant mesothelioma remains a diagnostic challenge. Sequential use of BAP1 immunohistochemistry and CDKN2A fluorescence in situ hybridization is specific for diagnosis of mesothelioma, but fluorescence in situ hybridization is both costly and time-consuming. Early data indicate that mesothelioma shows extensive loss of nuclear 5-hydroxymethylcytosine (5-hmC). We studied 49 cases of mesothelioma (17 epithelioid mesothelioma, 22 biphasic mesothelioma, and 10 sarcomatoid mesothelioma) and 23 benign mesothelial proliferations using a 5-hmC single immunohistochemical stain, CAM5.2/5-hmC double immunohistochemical stain, and BAP1 immunohistochemistry. Estimations of extent of 5-hmC loss were made using the 5-hmC single stain and CAM5.2/5-hmC double stain, and extent of nuclear 5-hmC loss was definitively quantitated in at least 1000 cells per case. Mean nuclear 5-hmC loss in mesothelioma (84%) was significantly greater than in benign mesothelial proliferations (4%) (p 0.0001). Using 5-hmC loss in 50% of tumor nuclei to define the diagnosis of mesothelioma, 5-hmC immunohistochemistry showed sensitivity of 92% and specificity of 100%. An immunopanel including 5-hmC and BAP1 immunohistochemistry achieved sensitivity of 98% and specificity of 100%. Extensive nuclear 5-hmC loss is sensitive and specific for mesothelioma in the differential diagnosis with benign mesothelial proliferations. In challenging mesothelial lesions, immunohistochemical studies showing either extensive 5-hmC loss or BAP1 loss indicate a diagnosis of mesothelioma, precluding the need for CDKN2A fluorescence in situ hybridization in a considerable number of cases.

The pathologist plays a central role in the diagnosis and management of malignant mesothelioma, including definitive tissue-based diagnosis in conjunction with clinical and radiographic data; diverse ancillary studies of diagnostic, prognostic, and predictive importance; and research efforts to better define the pathobiology of mesothelioma and develop novel clinical applications. The pivotal role of pathology in care of mesothelioma patients was on display at the recent meeting of the International Mesothelioma Interest Group (iMig) in Ottawa, Canada. This review summarizes the key findings of the "Molecular Pathways and Diagnosis in Malignant Mesothelioma" plenary session, including a large multi-institutional validation of a composite nuclear grading system for pleural mesothelioma, including incorporation of tumor necrosis as an additional independent prognostic factor; the correlation between nuclear grading in small biopsies and paired resection specimens in pleural mesothelioma; a multi-institutional study of important clinical and pathologic prognostic factors in peritoneal mesothelioma; the diagnostic role of HEG1 immunohistochemistry as a highly sensitive and specific marker of mesothelial lineage; the prevalence and diagnostic significance of MET protein overexpression in mesothelioma, as well as the correlation between MET protein overexpression and MET gene amplification; and the prognostic role of EZH2 protein overexpression in mesothelioma, together with data indicating an important pathogenic role for EZH2 in mesothelioma tumorigenesis. Special consideration is given to the convergence of diagnostic, prognostic, and predictive tools and their role in guiding highly personalized patient-centered management, and to the translation of novel research findings to practical techniques for routine pathologic practice.

Objectives Numerous studies on malignant mesothelioma (MM) highlight the prognostic importance of histologic subtype, nuclear grade, and necrosis. This study compares these parameters in paired biopsy and resection specimens of pleural MM. Methods Histologic subtype, percentage of epithelioid morphology, nuclear grade, and the presence or absence of necrosis were compared in 429 paired biopsies and resection specimens of pleural MM from 19 institutions. Results Histologic subtype was concordant in 81% of cases (κ = 0.58). When compared with resection specimens, epithelioid morphology at biopsy had a positive predictive value (PPV) of 78.9% and a negative predictive value (NPV) of 93.5%; sarcomatoid morphology showed high PPV (92.9%) and NPV (99.3%), and biphasic morphology PPV was 89.7% and NPV was 79.7%. Agreement of the percentage of epithelioid morphology was fair (κ = 0.27). Nuclear grade and necrosis were concordant in 75% (κ = 0.59) and 81% (κ = 0.53) of cases, respectively. Nuclear grade showed moderate (κ = 0.53) and substantial (κ = 0.67) agreement from patients with and without neoadjuvant therapy, respectively, and necrosis showed moderate (κ = 0.47 and κ = 0.60) agreement, respectively, in the same subsets of paired specimens. Conclusions Paired biopsy-resection specimens from pleural MM show overall moderate agreement in pathologic parameters. These findings may help guide postbiopsy management and triage of patients with MM.

Aims Methylthioadenosine phosphorylase (MTAP) immunohistochemical expression is a specific marker of CDKN2A deletion in malignant mesothelioma. However, the relationship of MTAP expression with MTAP copy number remains unexplored. Methods and results Forty malignant pleural mesotheliomas were characterised by targeted next-generation sequencing (29), single-nucleotide polymorphism microarray (seven), or both (four). MTAP and CDKN2A copy numbers were correlated with MTAP expression. Twenty-seven (68%) tumours showed CDKN2A deletion (14 heterozygous; 13 homozygous), of which 20 (74%) showed MTAP codeletion (15 heterozygous; five homozygous). No tumours showed MTAP deletion without CDKN2A codeletion. Loss of MTAP expression was seen in 16 (40%) tumours, and was 75% sensitive and 95% specific for MTAP deletion, and 59% sensitive and 100% specific for CDKN2A deletion. Nine of 40 (23%) tumours showed heterogeneous MTAP staining, and the percentage of tumour cells with MTAP loss correlated with molecular detection of MTAP deletion. Conclusions MTAP is frequently codeleted with CDKN2A in pleural mesothelioma. However, homozygous deletion of both genes occurs in a minority of tumours (5/40; 13%); CDKN2A deletion often co-occurs with heterozygous MTAP deletion or neutral MTAP copy number; and MTAP expression correlates inconsistently with heterozygous MTAP deletion. Correspondingly, MTAP immunohistochemistry is a highly specific but only moderately sensitive assay for CDKN2A deletion.

Mesenchymal lesions of the vulva include site-specific entities limited to the lower genital tract, as well as a range of non-site-specific tumors that are more common at extragenital sites. Site-specific lesions include fibroepithelial stromal polyp, cellular angiofibroma, angiomyofibroblastoma, and aggressive angiomyxoma. Non-site-specific tumors that may occur in the vulva include those of smooth muscle, skeletal muscle, vascular, neural, adipocytic, and uncertain differentiation. This review discusses both site-specific and non-site-specific vulvar mesenchymal lesions including non-neoplastic proliferations, benign neoplasms, locally aggressive neoplasms with a predilection for local recurrence, neoplasms of indeterminate biologic potential, and frankly malignant neoplasms with a high risk of distant metastasis and death. Accurate diagnosis is essential for proper management, and is facilitated by correlation with clinical findings and targeted application of immunohistochemical and molecular studies.

INTRODUCTION: Histologic subtypes of malignant pleural mesothelioma are a major prognostic indicator and decision denominator for all therapeutic strategies. In an ambiguous case, a rare transitional mesothelioma (TM) pattern may be diagnosed by pathologists either as epithelioid mesothelioma (EM), biphasic mesothelioma (BM), or sarcomatoid mesothelioma (SM). This study aimed to better characterize the TM subtype from a histological, immunohistochemical, and molecular standpoint. Deep learning of pathologic slides was applied to this cohort. METHODS: A random selection of 49 representative digitalized sections from surgical biopsies of TM was reviewed by 16 panelists. We evaluated BAP1 expression and CDKN2A (p16) homozygous deletion. We conducted a comprehensive, integrated, transcriptomic analysis. An unsupervised deep learning algorithm was trained to classify tumors. RESULTS: The 16 panelists recorded 784 diagnoses on the 49 cases. Even though a Kappa value of 0.42 is moderate, the presence of a TM component was diagnosed in 51%. In 49% of the histological evaluation, the reviewers classified the lesion as EM in 53%, SM in 33%, or BM in 14%. Median survival was 6.7 months. Loss of BAP1 observed in 44% was less frequent in TM than in EM and BM. p16 homozygous deletion was higher in TM (73%), followed by BM (63%) and SM (46%). RNA sequencing unsupervised clustering analysis revealed that TM grouped together and were closer to SM than to EM. Deep learning analysis achieved 94% accuracy for TM identification. CONCLUSION: These results revealed that the TM pattern should be classified as non-EM or at minimum as a subgroup of the SM type. ispartof: JOURNAL OF THORACIC ONCOLOGY vol:15 issue:6 pages:1037-1053 ispartof: location:United States status: published

BACKGROUND: Despite routine use of echocardiographic parameters to evaluate the severity of cardiac amyloidosis (CA), this methodology has not been well validated. We developed a histopathologic schema for quantifying CA burden and evaluated its relationship with clinical outcomes. Additionally, echocardiographic parameters were tested as potential noninvasive indices of CA burden. METHODS: We retrospectively studied 59 patients with CA (17 light chain, 42 transthyretin) who underwent endomyocardial biopsies. Light microscopy with staining was used to categorize CA burden as mild-to-moderate (

BACKGROUND Autoantibodies against Factor VIII (FVIII) define the rare but life-threatening bleeding disorder acquired hemophilia A (AHA). Correction of FVIII deficiency and eradication of the factor inhibitor are the ultimate therapeutic goals in this disorder. Bypassing agents such as recombinant factor VIIa (rFVIIa) or FVIII inhibitor bypassing agent are often used to control coagulopathy before the inhibitor is eradicated. Bypassing agents carry a risk of thrombosis, however. CASE REPORT We report a patient with newly diagnosed AHA and thalamic bleed who additionally had active atrial fibrillation and developed a segmental pulmonary embolism, limiting tolerable rFVIIa dosage. This patient with very-high-risk brain bleed and concurrent thrombosis on bypass agent represented a significant management dilemma for which we successfully utilized therapeutic plasma exchange (TPE) to reduce the inhibitor titer. RESULTS FVIII inhibitor was undetectable and FVIII level was above the lower limit of normal within 12.5 days from starting TPE. While the patient ultimately died 24 days from admission for reasons unrelated to bleeding, his intracerebral hemorrhage was unchanged in size and no other bleeding morbidity was observed. CONCLUSION This patient achieved eradication of FVIII inhibitor and did not have bleed expansion while receiving multimodal therapy including corticosteroids, rituximab, and TPE. We discuss the periprocedural risks of TPE in an acquired hemophilia patient and our multiteam management of that risk.

The Chicago Consensus Working Group provides multidisciplinary recommendations for the management of peritoneal mesothelioma. These guidelines are developed with input from leading experts, including surgical oncologists, medical oncologists, pathologists, radiologists, palliative care physicians, and pharmacists. These guidelines recognize and address the emerging need for increased awareness of the appropriate management of peritoneal surface disease. They are not intended to replace the quest for higher levels of evidence.

The Chicago Consensus Working Group provides multidisciplinary recommendations for the management of ovarian neoplasms specifically related to the management of peritoneal surface malignancy. These guidelines are developed with input from leading experts, including surgical oncologists, medical oncologists, gynecologic oncologists, pathologists, radiologists, palliative care physicians, and pharmacists. These guidelines recognize and address the emerging need for increased awareness in the appropriate management of peritoneal surface disease. They are not intended to replace the quest for higher levels of evidence.

Atypical hyperplasia/endometrial intraepithelial neoplasia is an accepted precursor to endometrioid-type endometrial carcinoma. Mismatch repair-deficient endometrial carcinomas are also known to be a biologically and clinically distinct subset of tumors. However, the development of microsatellite instability in endometrial carcinogenesis has not yet been evaluated by novel next-generation sequencing-based methods. We examined 17 mismatch repair-deficient endometrioid endometrial carcinomas and their paired atypical hyperplasia/endometrial intraepithelial neoplasia precursors using a next-generation sequencing panel with quantitative microsatellite instability detection at 336 loci. Findings were compared to histological features, polymerase chain reaction-based microsatellite instability testing, immunohistochemical expression of mismatch repair proteins, and tumor mutational burden calculations. All 17 endometrial carcinomas and 8/17 atypical hyperplasia/endometrial intraepithelial neoplasia showed microsatellite instability by next-generation sequencing-based testing. Endometrial carcinoma specimens showed significantly more unstable microsatellite loci than paired atypical hyperplasia/endometrial intraepithelial neoplasia (mean: 40.0% vs 19.9 unstable loci, respectively). Out of nine microsatellite-stable atypical hyperplasia/endometrial intraepithelial neoplasia specimens, four showed mismatch repair loss by immunohistochemistry. All atypical hyperplasia/endometrial intraepithelial neoplasia and endometrial carcinoma specimens with microsatellite instability were also mismatch repair-deficient by immunohistochemistry. Tumor mutational burden was significantly greater in endometrial carcinoma than in paired atypical hyperplasia/endometrial intraepithelial neoplasia specimens, and tumor mutational burden was significantly correlated with percent unstable microsatellite loci. Paired atypical hyperplasia/endometrial intraepithelial neoplasia and endometrial carcinoma specimens show progressive accumulation of unstable microsatellite loci following loss of mismatch repair protein expression. Comprehensive next-generation sequencing-based testing of endometrial carcinomas offers new insights into endometrial carcinogenesis and opportunities for improved tumor surveillance, diagnosis, and management.

We present an instructive case of FIGO grade 1 endometrioid endometrial carcinoma with a biphasic morphology, corresponding to subclonal loss of mismatch repair proteins (MMRP) MLH1 and PMS2 by immunohistochemistry and subclonal microsatellite instability. A pulmonary metastasis represented only the tumor component with retention of MMRPs. This case illustrates the need for pathologists to recognize and report heterogenous expression of MMRPs in endometrial carcinoma, to consider tumor heterogeneity when selecting foci for molecular studies, and to re-evaluate MMRP expression in tumor metastases, when clinically indicated. These considerations are particularly important as the relevance of MMRP expression in endometrial cancer expands beyond Lynch syndrome screening, into a new role as a predictive marker for immunotherapy.

Summary Malignant mesothelioma (MM) is an aggressive neoplasm with poor prognosis. The Dako PD-L1 22C3 and 28-8 pharmDx assays are approved by the US Food and Drug Administration (FDA) as companion and complementary diagnostics for the anti–PD-1 drugs pembrolizumab and nivolumab, respectively. Data from multiple clinical trials indicate that immunotherapy has antitumor activity in advanced malignant pleural (MPM) and peritoneal mesothelioma (MPeM). However, large studies of PD-L1 expression in MM using the FDA-approved anti–PD-L1 assays are lacking. We stained tissue microarray sections (N = 125; 112 MPM and 13 MPeM) using 2 FDA-approved clinical immunohistochemical makers for PD-L1 expression: Dako PD-L1 22C3 pharmDx and Dako PD-L1 28-8 pharmDx. Overall, 22% (27/125) of MMs were positive using the 22C3 assay, whereas 27% (32/117) were positive using the 28-8 assay, using a tumor proportion score cutoff of 1%. Tumor cell PD-L1 expression was strongly correlated with PD-L1 expression on tumor-associated immune cells. No significant difference in PD-L1 expression was observed by patient sex, age, treatment history, pathologic stage, or histologic subtype. However, the proportion of cases positive for PD-L1 expression was higher among MPeM compared to MPM (P = .007 for 22C3 assay; P = .04 for 28-8 assay). PD-L1 is expressed in a substantial proportion of MM cases, as measured by FDA-approved companion assays for widely used immunotherapeutic drugs. PD-L1 expression is particularly prevalent in MPeM. These findings support large clinical studies to further examine PD-L1 as a biomarker for a subset of MM patients that may benefit from immunotherapy.

Mucolipidosis type II, also known as I-cell disease, is an autosomal recessive inborn error of metabolism, resulting from loss-of-function mutations in GNPTAB. Affected infants exhibit multiple physical anomalies and developmental delay, and death from disease follows in early childhood. Here we present an instructive case of mucolipidosis type II affecting 1 fetus and placental disk in a dichorionic-diamnionic twin pregnancy delivered at 36-wk gestation. The second twin and placental disk showed no abnormality. On microscopic examination, the affected placenta displayed marked vacuolization of the syncytiotrophoblast and Hofbauer cells, which was confirmed on ultrastructural examination. To our knowledge, this is the first description of placental findings in a twin pregnancy, wherein only 1 twin is affected by an inborn error of metabolism. This provides an opportunity to highlight the placental abnormalities seen in this group of diseases, and to emphasize the role of pathologic examination in early detection of otherwise unsuspected inborn errors of metabolism.

Objective Universal screening of endometrial cancer (EC) for Lynch syndrome (LS) has been increasingly implemented in the past five to ten years. Most pathologists initiate screening with immunohistochemistry (IHC) for mismatch repair proteins (MMRPs), using either pre-surgical samplings (endometrial biopsy or curettage, EMB/C) or hysterectomy specimens. We report a systematic assessment of the equivalence of IHC for LS screening on EMB/C versus hysterectomy specimens. Methods We identified 99 patients diagnosed with endometrioid EC and performed IHC for MMRPs MLH1, MSH2, MSH6, and PMS2 on their diagnostic EMB/C and paired hysterectomy specimen. Each specimen was scored as MMRP-retained or MMRP-deficient. Results Ninety-one EMB/Cs had carcinoma, while 8 EMB/Cs showed only complex atypical hyperplasia (CAH). Carcinoma was identified in all 99 hysterectomy specimens. Considering all 99 patients tested, concordance of MMRP expression pattern between EMB/C and paired hysterectomy specimen was 100%. Sixty-nine cases retained all four MMRPs, while 30 were MMRP deficient (26 MLH1- and PMS2-deficient, 3 MSH2- and MSH6-deficient, 1 PMS2-deficient). Conclusions In screening for LS in EC, IHC for MMRPs can be performed with identical accuracy on either EMB/C or hysterectomy specimens. Routine testing of diagnostic EMB/Cs may lead to earlier detection of MMRP deficiency, with improved patient uptake of genetic counseling and potential for earlier identification of immunotherapy candidates. Furthermore, reliable IHC-based LS screening performed on EMB/C can guide patient management and genetic counseling in patients unable to undergo hysterectomy.

Distinguishing malignant peritoneal mesothelioma (MPM) from serous carcinoma involving the peritoneum remains a diagnostic challenge, particularly in small biopsy and cytology specimens. In this distinction, PAX8 expression has been regarded as a specific marker of serous carcinoma. In addition, BAP1 loss is reportedly specific to MPM, in the distinction from both benign mesothelial lesions and ovarian serous tumors (OSTs). Using immunohistochemistry, we examined PAX8 and BAP1 expression in 27 MPMs, 25 cases of benign mesothelium, and 45 OSTs. Five MPMs were PAX8 (5/27, 18%), while 8 cases of benign mesothelium expressed PAX8 (8/25, 32%). PAX8 expression in mesothelium was significantly more common in women than in men (P=0.01). Sixteen MPMs exhibited BAP1 loss (16/25, 64%), while BAP1 was retained in all benign mesothelium and all OSTs. All cases of PAX8 mesothelium were negative for expression of estrogen receptor. These data show that PAX8 is expressed in both benign and malignant mesothelium, and that BAP1 loss is highly specific for MPM, in the differential with both benign mesothelial proliferations and OTSs. These results also have implications for primary diagnosis and for pathologic staging of OST. Caution should be applied when PAX8 expression is used to distinguish mesothelial and serous proliferations, and BAP1 loss may be confirmatory in cases where mesothelioma is favored.

Acute-onset heart failure in a young, otherwise healthy patient can be due to either acquired or congenital etiologies. While some diagnoses carry specific histologic hallmarks, many causes of myocardial injury culminate in the relatively nonspecific morphologic pattern of dilated cardiomyopathy. In such cases, a broad differential diagnosis and close clinicopathologic correlation are essential. Here we describe the acute and chronic histologic features of heart failure arising in the context of long-standing abuse of cocaine, alcohol, and marijuana. The mechanisms of cardiotoxicity are discussed for each drug, with particular emphasis on the amplified cardiac injury caused by concomitant cocaine and alcohol use. Although its histologic features are themselves nonspecific, correlation with clinical history, targeted studies to exclude alternative diagnoses, and careful morphologic examination permit confident diagnosis of cardiomyopathy secondary to polysubstance abuse.