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Introduction: Although alterations in SMARCA4‐deficient occur in non–small cell lung carcinoma (SD‐NSCLC), thoracic SMARCA4‐deficient undifferentiated tumor (TSDUT) is recognized as a distinct entity in the 2021 World Health Organization Classification of Thoracic Tumors because of unique morphologic, immunophenotypic and molecular features, and worse survival compared with SD‐NSCLC. Cytologic diagnosis of TSDUT is clinically important because of its aggressive behavior and because it is often diagnosed by fine‐needle aspiration because TSDUTs are usually unresectable at presentation. Here, we identify cytologic features that can be used for recognition of TSDUT and distinction from SD‐NSCLC. Materials and Methods: Cytomorphologic features were investigated in cytology specimens from patients with TSDUT (n = 11) and compared with a control group of patients with SD‐NSCLC (n = 20). Results: The presence of classic rhabdoid morphology, at least focally, was entirely specific for TSDUT (n = 6, 55%) compared with SD‐NSCLC (n = 0) in this study. TSDUT more frequently showed tumor necrosis (n = 11, 100% vs. n = 8, 40%; p =.001), dominant single‐cell pattern on aspirate smears or touch preparation slides (n = 8 [of 9], 80% vs. n = 3, 15%; p =.010), nuclear molding (n = 5, 45% vs. n = 1, 5%; p =.013), and indistinct cell borders (n = 11, 100% vs. n = 5, 25%; P <.001) compared with SD‐NSCLC, respectively. Conclusions: Cytomorphologic features occurring more frequently in TSDUT include tumor necrosis, dominant single‐cell pattern, nuclear molding indistinct cell borders, and focal rhabdoid cells. Presence of these features in a cytology specimen of an undifferentiated tumor, particularly in a patient with a thoracic mass, should raise suspicion for TSDUT and prompt appropriate ancillary workup. Cytomorphologic features occurring more frequently in thoracic SMARCA4‐deficient undifferentiated tumor (TSDUT) include tumor necrosis, dominant single‐cell pattern, nuclear molding, indistinct cell borders, and/or rhabdoid cells. Presence of these features in a cytology specimen of an undifferentiated tumor, particularly in a patient with a thoracic mass, should raise suspicion for TSDUT and prompt appropriate ancillary workup for this diagnosis. [ABSTRACT FROM AUTHOR]

Background: The World Health Organization incorporates morphologic features with prognostic significance in the 2021 classification of epithelioid diffuse pleural mesothelioma (E‐DPM). Although cytology specimens are often the first and occasionally the only specimen available for patients with DPM, these features have not yet been investigated in cytology. Methods: Nuclear atypia, pleomorphic features, necrosis, and architectural patterns were retrospectively assessed in 35 paired cytology and concurrent/consecutive surgical pathology specimens of E‐DPM. Agreement between pairs was determined via unweighted κ scores. Discordant cases were re‐reviewed to determine the reasons for disagreement. Results: Interpretation of nuclear atypia in cytology was concordant with histology in all cases (κ = 1.000; p <.001). The presence of pleomorphic features and necrosis was concordant in 97.1% (κ = 0.842; p <.001) and 85.7% (κ = 0.481; p =.001) of paired cases, respectively. Assessment of architectural patterns in cytology showed only slight agreement with histology (κ = 0.127; p =.037). In cytology cases (n = 23) with cell block material available, assessment of nuclear atypia and the presence of pleomorphic features showed perfect agreement (κ = 1.000; p <.001, each), the presence of necrosis showed moderate agreement (κ = 0.465; p =.008), and assessment of architectural patterns showed slight agreement (κ = 0.162; p =.15) in paired specimens. Most disagreements were due to sampling differences between cytology and histology specimens. Conclusions: Although complete nuclear grading of E‐DPM is not possible given the unreliability of mitotic counts in cytology, assessment of nuclear atypia in cytology specimens is shown to be reliable. Identification of pleomorphic features and necrosis is also reliable despite occasional sampling issues. Assessment of architectural patterns is more limited in cytology. Assessment of morphologic features that are prognostically significant in epithelioid pleural mesothelioma, including nuclear atypia and the presence of necrosis and pleomorphic cytologic features, can be reliably performed in cytology. Reporting these features in cytology reports could provide prognostic information for patients unable to undergo tissue biopsies. [ABSTRACT FROM AUTHOR]

Thyroid transcription factor 1 (TTF1) and p40 are widely-utilized diagnostic markers of lung adenocarcinoma (LUAD) and squamous cell carcinoma (LUSC), respectively. Diffuse coexpression of TTF1 and p40 has been described in only rare case reports. In a multiinstitutional study, we collected the largest cohort of these unusual tumours to-date (n = 14), with the goal of elucidating their clinicopathological and genomic characteristics. Lung tumours with diffuse coexpression (labelling 50–100% tumour cells) of TTF1 clone 8G7G3/1 and p40 clone BC28 were identified. Detailed clinicopathological and immunohistochemical parameters were analyzed. Eight tumours were analyzed by next-generation sequencing (NGS) and the results were compared to those in > 9 K LUAD and > 1 K LUSC. All tumours with diffuse TTF1/p40 coexpression were poorly differentiated non-small cell lung carcinomas (NSCLC), 42% of which had basaloid features. Some tumours exhibited focal keratinization (14%), napsin A and/or mucicarmine labelling (46%) or both squamous and glandular features (7%). NGS revealed a uniquely high rate of FGFR1 amplifications (70%) compared to either LUAD (0.7%, P < 0.0001) or LUSC (11%, P = 0.001). LUAD-type targetable driver alterations were identified in 38% of cases (one EGFR, two KRAS G12C). The tumours were clinically aggressive, exhibiting metastatic disease in most patients. Lung carcinomas with diffuse TTF1/p40 coexpression represent poorly differentiated NSCLCs with frequent basaloid features, but some show evidence of focal squamous, glandular or dual differentiation with a distinctly high rate of FGFR1 amplifications. The presence of targetable LUAD-type alterations (EGFR, KRAS G12C) emphasizes the importance of molecular testing in these tumours. [ABSTRACT FROM AUTHOR]

Aims: To improve understanding of the pathology of immune check‐point inhibitor (ICI)‐related pneumonitis, clinical, radiographic and histopathological features and outcomes were investigated in a cohort of patients who were treatment‐naive before receiving ICI inhibition, who underwent lung biopsy, and in whom other potential causes of lung injury were excluded. Methods: Patients were retrospectively identified via searches of institutional pathology and clinical records. Patients treated with other modalities for cancer and patients with lung infections or other aetiologies that could cause pneumonitis were excluded. Clinical records were reviewed by pulmonologists. Imaging studies at presentation and follow‐up were reviewed by a thoracic radiologist. Pathology was reviewed by thoracic pathologists. Results: Six patients with ICI‐related pneumonitis were identified. Two patients presented with respiratory failure requiring mechanical ventilation, diffuse ground glass opacities (GGOs) on chest computed tomography (CT) and acute lung injury (ALI) pattern on transbronchial lung biopsies and had fatal outcomes, despite treatment. The remaining four patients presented with less severe symptoms, predominantly consolidations and patchy ground glass and part solid opacities on chest CT, organising pneumonia (OP) or chronic interstitial inflammation histologically, and showed favourable responses to treatment and remission within months. Conclusions: This study highlights two radiological–pathological patterns of ICI‐related pneumonitis with different behaviour: (1) severe respiratory symptoms and diffuse GGOs on imaging correlating with ALI pattern histologically and poor prognosis; and (2) mild respiratory symptoms and consolidations or patchy subsolid opacities on imaging correlating histologically with OP or chronic interstitial inflammation and good outcomes. [ABSTRACT FROM AUTHOR]

Introduction: We describe post‐mortem pulmonary histopathologic findings of COVID‐19 pneumonia in patients with a spectrum of disease course, from rapid demise to prolonged hospitalisation. Methods and results: Histopathologic findings in post‐mortem lung tissue from eight patients who died from COVID‐19 pneumonia were reviewed. Immunohistochemistry (IHC) and next‐generation sequencing (NGS) were performed to detect virus. Diffuse alveolar damage (DAD) was seen in all cases with a spectrum of acute phase and/or organising phase. IHC with monoclonal antibodies against SARS‐CoV‐2 viral nucleoprotein and spike protein detected virus in areas of acute but not organising DAD, with intracellular viral antigen and RNA expression seen predominantly in patients with duration of illness less than 10 days. Major vascular findings included thrombi in medium‐ and large‐calibre vessels, platelet microthrombi detected by CD61 IHC and fibrin microthrombi. Conclusions: Presence of SARS‐CoV‐2 viral RNA by NGS early in the disease course and expression of viral antigen by IHC exclusively in the acute, but not in the organising phase of DAD, suggests that the virus may play a major role in initiating the acute lung injury of DAD, but when DAD progresses to the organising phase the virus may have been cleared from the lung by the patient's immune response. These findings suggest the possibility of a major change during the disease course of COVID‐19 pneumonia that may have therapeutic implications. Frequent thrombi and microthrombi may also present potential targets for therapeutic intervention. [ABSTRACT FROM AUTHOR]

Background: Sclerosing pneumocytoma (SP) is a rare, benign pulmonary neoplasm. To the authors' knowledge, the current study is the first to evaluate the cytomorphology and immunoprofile of SP in a series. Methods: A total of 9 fine‐needle aspiration cases of SP (7 of which were computed tomography guided and 2 of which were endobronchial ultrasound guided) including histopathology and immunohistochemistry were collected from 5 institutions. Results: The female‐to‐male ratio was 3.5:1, and the mean age of the patients was 54 years (range, 27‐73 years). All cases presented as lung nodules, with a mean size of 2.2 cm (range, 1.1‐5 cm), and were interpreted as atypical on rapid on‐site evaluation. The final diagnoses were favor adenocarcinoma (1 case), well‐differentiated lung adenocarcinoma (2 cases), low‐grade epithelial neoplasm (2 cases), and sclerosing pneumocytoma (4 cases). Samples were moderately cellular, and consisted of round epithelioid cells with clear cell features, columnar cells, and spindle cells. A papillary arrangement with prominent hyalinized fibrovascular cores was the most common architectural pattern, followed by flat sheets and acinar formations. Tumor cells demonstrated mild, focally moderate nuclear pleomorphism with prominent nucleoli, hyperchromasia, nuclear elongation, nuclear overlap, and occasional nuclear inclusions and grooves. The background consisted of foamy macrophages (9 cases), hemosiderin pigment (6 cases), and lymphoid aggregates (3 cases) with no mitoses and/or necrosis. The surface cells and underlying round cells were positive for both thyroid transcription factor 1 and epithelial membrane antigen in all cases, which was the most notable immunohistochemical finding. Conclusions: Cytomorphological findings of SP overlap with those of well‐differentiated lung adenocarcinoma. Awareness of these cytomorphologic findings and the distinct immunoprofile of the 2 cell types found in SP should prevent a misdiagnosis and aggressive treatment. Sclerosing pneumocytoma (SP) is a rare, benign, pulmonary neoplasm of primitive respiratory epithelial origin that shares cytomorphologic features with well‐differentiated lung adenocarcinoma. A papillary arrangement with prominent hyalinized fibrovascular cores, flat sheets, and acinar formations composed of round epithelioid cells with clear cell features, columnar cells, and spindle cells with immunoreactivity of surface cells and underlying round cells for both thyroid transcription factor 1 and epithelial membrane antigen are features distinguishing SP from lung adenocarcinoma. [ABSTRACT FROM AUTHOR]

Background: The Ki‐67 proliferation marker has multiple diagnostic and prognostic applications. Although several clones to the Ki‐67 antigen are commercially available, the MIB1 clone is widely recommended in the surgical pathology literature for neuroendocrine tumors. In our cytopathology practice, we have encountered unexpectedly low MIB1 immunoreactivity in CytoLyt‐fixed cell blocks (CBs). The current study evaluated the impact of fixatives, CB processing, and immunocytochemical (ICC) procedures on Ki‐67 immunoreactivity. Methods: Test CBs were prepared from freshly resected tumors, and multiple variables in the MIB1 ICC procedure were tested, including CytoLyt versus formalin collection media, MIB1 versus other Ki‐67 clones including 30‐9, and other variables. MIB1 versus Ki‐67 30‐9 clones were tested in parallel on CytoLyt‐fixed CBs from clinical samples of small cell lung carcinoma (SCLC). Results: In the test CBs (n = 10), the mean MIB1 labeling index was 10% in CytoLyt versus 47% in formalin (P = .0116), with a mean loss of reactivity in matched CBs of 37% (up to 70%). None of the procedure modifications tested in 223 individual ICC reactions recovered MIB1 reactivity in CytoLyt except for switching to the Ki‐67 30‐9 antibody. In CytoLyt‐fixed SCLC samples (n = 14), the Ki‐67 30‐9 antibody demonstrated expected ranges of reactivity (mean, 83%; range, 60%‐100%), whereas MIB1 demonstrated markedly inhibited labeling (mean, 60%; range, 10%‐95%) (P = .0058). Conclusions: CytoLyt fixation substantially inhibits MIB1 immunoreactivity, whereas the Ki‐67 30‐9 clone is not susceptible to inhibition. Markedly discrepant MIB1 reactivity may present a pitfall in the diagnosis of SCLC and may lead to the incorrect prognostic stratification of other tumor types. For laboratories using CytoLyt, we recommend using the Ki‐67 30‐9 antibody rather than the MIB1 antibody. CytoLyt fixation substantially inhibits MIB1 immunoreactivity and may present a diagnostic pitfall in certain tumors, especially small cell carcinoma. The Ki‐67 30‐9 clone demonstrates adequate performance and should be the clone of choice in laboratories using CytoLyt collection media. [ABSTRACT FROM AUTHOR]

With an escalating number of predictive biomarkers emerging in non–small cell lung carcinoma (NSCLC), immunohistochemistry (IHC) is being used as a rapid and cost‐effective tool for the screening and detection of many of these markers. In particular, robust IHC assays performed on formalin‐fixed, paraffin‐embedded (FFPE) tumor tissue are widely used as surrogate markers for ALK and ROS1 rearrangements and for detecting programmed death ligand 1 (PD‐L1) expression in patients with advanced NSCLC; in addition, they have become essential for treatment decisions. Cytology samples represent the only source of tumor in a significant proportion of patients with inoperable NSCLC, and there is increasing demand for predictive biomarker testing on them. However, the wide variation in the types of cytology samples and their preparatory methods, the use of alcohol‐based fixatives that interfere with immunochemistry results, the difficulty in procurement of cytology‐specific controls, and the uncertainty regarding test validity have resulted in underutilization of cytology material for predictive immunocytochemistry (ICC), and most cytopathologists limit such testing to FFPE cell blocks (CBs). The purpose of this review is to: 1) analyze various preanalytical, analytical, and postanalytical factors influencing ICC results; 2) discuss measures for validation of ICC protocols; and 3) summarize published data on predictive ICC for ALK, ROS1, EGFR gene alterations and PD‐L1 expression on lung cancer cytology. Based on our experience and from a review of the literature, we conclude that cytology specimens are in principal suitable for predictive ICC, but proper optimization and rigorous quality control for high‐quality staining are essential, particularly for non‐CB preparations. There is increasing demand for predictive biomarker testing on cytology samples in patients with lung cancer, and such predictive immunocytochemistry (ICC) is largely limited to cell blocks (CBs). An analysis of various factors influencing ICC and a review of the published literature reveals that cytology specimens are principally suitable for predictive ICC, but proper optimization and rigorous quality control are essential, particularly for non‐CB preparations. [ABSTRACT FROM AUTHOR]

Background: Histological features and Ki-67 index have known usefulness in predicting prognosis and guiding therapy among patients with metastatic pancreatic neuroendocrine neoplasms. Fine-needle aspiration may offer advantages for Ki-67 assessment because the technique obtains highly cellular, well-preserved specimens with the potential for broader tumor sampling. In the current study, the authors evaluated concordance for grade and differentiation between concurrent core needle biopsy and cytology preparations. Cytological features and grade then were correlated with survival.Methods: Differentiation, grade by Ki-67 index, and correlation of these features with survival were compared between concurrent core needle biopsy and cytology specimens from 44 patients with metastatic pancreatic neuroendocrine neoplasms.Results: Differentiation by cytology smear resulted in 38 cases of well (86%) and 6 cases of poor (14%) differentiation. Agreement for differentiation between smear and cell block, smear and core needle biopsy, and cell block and core needle biopsy was 88%, 94%, and 83%, respectively, and agreement for grade was 68%, 54%, and 22%, respectively. Cytology differentiation and cytology grade were found to be strong predictors of outcome with respective hazard ratios of 8.3 (95% confidence interval [95% CI], 3.1-22.1; P<.001) and 1.9 (95% CI, 1.2-2.9) for each ascending grade. The median disease-specific survival cytology projections were 121 months (95% CI, 57-185 months [estimated]) for grade 1, 45 months (95% CI, 29-87 months) for grade 2, and 19 months (95% CI, 1-44 months) for grade 3, with median survivals of 45 months and 3 months, respectively, for patients with well-differentiated and poorly differentiated neuroendocrine tumors (P<.001).Conclusions: Grading of pancreatic neuroendocrine neoplasms on cytology may not correlate exactly with concurrent core needle biopsy, but cytology differentiation and grade are predictive of survival based on stage-adjusted analysis. Cancer Cytopathol 2017;125:188-196. © 2016 American Cancer Society. [ABSTRACT FROM AUTHOR]

A case study is presented of a 73-year-old male patient who type A thyoma that presented as a bone metastasis. It states that a biopsy revealed that oval to spindle-shaped tumor cells had infiltrated the sample. It mentions that immunohistochemistry showed the expression of pan-cytokeratin by the tumor while next-generation sequencing revealed an HRAS p.Q61R mutation without structural variants or copy number alterations in metastasis.

Aims The IASLC/ ATS/ ERS classification of lung adenocarcinoma provides a prognostically significant histological subclassification. The aim of this study was to investigate the accuracy, limitations and interobserver agreement of frozen sections for predicting histological subtype. Methods and results Frozen section and permanent section slides from 361 resected stage I lung adenocarcinomas ≤3 cm in size were reviewed for predominant histological subtype and the presence or absence of lepidic, acinar, papillary, micropapillary and solid patterns. Fifty cases were additionally reviewed by three pathologists to determine interobserver agreement. To test the accuracy of frozen section in judging degree of invasion, five pathologists reviewed frozen section slides from 35 cases with a predominantly lepidic pattern. There was moderate agreement on predominant histological subtype between frozen sections and final diagnosis (κ = 0.565). Frozen sections had high specificity for micropapillary and solid patterns (94% and 96%, respectively), but sensitivity was low (37% and 69%, respectively). The interobserver agreement was satisfactory (κ > 0.6, except for the acinar pattern). Conclusions Frozen section can provide information on the presence of aggressive histological patterns-micropapillary and solid-with high specificity but low sensitivity. It was difficult to predict the predominant pattern on the basis of frozen sections, mostly because of sampling issues. [ABSTRACT FROM AUTHOR]

BACKGROUND Touch preparations (TPs) can be performed for on-site adequacy assessment of core needle biopsies (CNBs). Although TPs can play a role in decreasing the number of nondiagnostic core biopsies, the impact of TPs on CNB has not been extensively evaluated. METHODS Computerized tomography-guided CNBs performed in a tertiary cancer center were retrospectively identified. On-site adequacy assessment was performed in all cases. The matching TPs and CNBs were evaluated for diagnostic accuracy of the TP. The relation between the site of biopsy and the cellularity of the CNB was also analyzed. RESULTS A total of 1100 CNB cases with associated TPs were identified over a 6-month period. Eighty-four cases (8%) showed marked differences in cellularity between CNB and TP, and 43 of these 84 cases (4.3%) showed the presence of diagnostic cells in either CNB or TP, but not in both. Lung was the biopsy site where CNB was most affected by loss of diagnostic cells. CONCLUSIONS TP and CNB findings must be integrated to prevent a misdiagnosis. Lung CNBs were more frequently affected by performing TPs. Cancer (Cancer Cytopathol) 2014;122:851-854. © 2014 American Cancer Society. [ABSTRACT FROM AUTHOR]

BACKGROUND A relative excess of nonneoplastic cells in frozen carcinoma samples is often a cause of false-negative results in molecular assays. Given the greater cohesiveness of epithelial tumor cells compared with nonneoplastic epithelium and mesenchymal stroma, the authors hypothesized that tumor procurement by touch imprinting would provide a simple, cost-effective method of obtaining enriched neoplastic cells compared with frozen whole-tumor samples. METHODS Eleven adenocarcinomas with known KRAS gene mutations were tested. Two sets of 8 touch imprint (TP) slides and 1 frozen whole-tumor sample (FS), both with a corresponding hematoxylin and eosin-stained slide, were obtained from each tumor. DNA from unstained TP and FS samples was tested for KRAS exon 2 mutations by Sanger sequencing. The percentage of carcinoma cells was determined by light microscopy of hematoxylin and eosin-stained slides. The fold increase in the mutant-enriched DNA in TP versus FS samples was determined by calculating the height ratio between the mutant and wild-type peaks on the sequencing electropherogram. RESULTS Using light microscopy, TP demonstrated a 1.1-fold to 3.5-fold (mean, 1.8-fold) enrichment in neoplastic cells compared with the FS. The mutant-to-wild-type peak height ratio was 1.4-fold to 7.1-fold (mean, 3.1-fold) higher in TP compared with the corresponding FS samples. The average amount of extracted DNA ranged from 145 ng to 7.9 μg per TP slide. CONCLUSIONS The procurement of carcinoma samples by TP is rapid, simple, and inexpensive; consistently provides a tumor-enriched sample; is an excellent source of high-quality tumor DNA; and could compensate for the relatively low sensitivity of direct sequencing. Cancer (Cancer Cytopathol) 2013;121:354-360. © 2013 American Cancer Society. [ABSTRACT FROM AUTHOR]

BACKGROUND: Pulmonary adenocarcinoma (AD) has a variety of architectural patterns. Recently, a 3-tiered histological pattern-based grading system was developed for stage I lung AD, stratifying patients into low, intermediate, and high risk for recurrence. However, cytology may serve as the primary method for diagnosis in patients with inoperable disease. Attempts to correlate architecture between parallel cytological and histological preparations have not been successful. Therefore, we evaluated cytomorphologic features of previously histologically graded AD to identify features of potential prognostic significance. METHODS: One hundred and thirteen fine-needle aspirations with excised adenocarcinomas were reviewed. In the liquid-based preparation, we evaluated cell arrangements (flat sheets vs 3-D clusters vs single cells), nuclear features (size variability, shape, and contour), nucleoli (prominent or inconspicuous), presence of nuclear inclusions, chromatin (fine, coarse, or clumped), and quality of background. The features were tested by multivariate analysis to identify associations with histological grade and disease-free survival (DFS), and a cytological score was generated. RESULTS: Nuclear size, chromatin pattern, and nuclear contours showed a significant association with histological grade and DFS. These features were included in the composite cytological score (range, 0-5). By grouping the cytological scores, we stratified the tumors into low (median DFS, 100%), intermediate (median DFS, 78%), and high (median DFS, 55%) rate of recurrence ( P = .008). There was a good correlation with the histological grading system. CONCLUSIONS: In liquid-based preparations, distinctive cytological features of pulmonary adenocarcinoma correlate with levels of histological differentiation and can be combined into a score with prognostic significance. Cancer (Cancer Cytopathol) 2012. © 2011 American Cancer Society. [ABSTRACT FROM AUTHOR]

An abstract of the article "Reliability of Cytologic Classification of Non-Small Cell Lung Cancer (NSCLC)," by Natasha Rekhtman, Maria A. Friedlander, Maureen F. Zakowski, and Andre L. Moreira is presented.

Background: Malignant solitary fibrous tumors (SFTs) are extremely uncommon and poorly understood mesenchymal neoplasms. There are only rare published accounts of the cytopathologic features of these tumors, prompting the current study., Design: All cases of malignant SFT with preoperative fine-needle aspirations (FNAs) from 1999 to 2008 were retrieved from the archives of 3 large teaching hospitals. FNA smears and cell block material including immunoperoxidase stains were reviewed, and the cytologic characteristics were described., Results: Thirteen cases of malignant SFT were identified in 11 patients. Mean age was 58 years, with a men:women ratio of 1:2.6. The tumors were generally large, with a mean size of 13.4 cm. Cytomorphologic features included mostly hypercellular smears with tissue fragments of monotonous, plump spindled cells with blunt-ended and indented nuclei and fragile, wispy cytoplasm. Also seen were bare nuclei, occasional mitoses, and rare necrosis. Some cases showed a predominance of epithelioid cells, whereas others displayed a loose myxomatous matrix. There was a general lack of single cells. None of the cases was diagnosed accurately as malignant SFT on FNA, and only 6 cases were called malignant or suspicious for malignancy., Conclusions: The FNA diagnosis of malignant SFT is extremely difficult and needs histologic material for accurate interpretation. Predominant FNA diagnoses were SFT or spindle cell neoplasm. Malignant SFT must be included in the differential diagnosis of a spindle cell neoplasm of any anatomic site, particularly if it displays features not typical of benign SFT. Immunoperoxidase staining has some utility, mainly in ruling out other neoplasms in the differential diagnosis., ((c) 2010 American Cancer Society.)