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Conventional chondrosarcoma is the most common primary malignant bone tumor in adults. Dedifferentiated chondrosarcomas represent 10 to 15% of conventional chondrosarcomas and constitute a high-grade subtype with a poor prognosis, with a 5-year survival rate of 24%. These tumors are characterized by a mutation in one of the isocitrate dehydrogenase (IDH) 1 or 2 genes in 70% of cases. Histological diagnosis requires a biphasic morphology combining a low-grade conventional chondrosarcoma component with a high-grade non-cartilaginous sarcomatoid component. In the literature, this dedifferentiated component most often corresponds to an osteosarcoma or an undifferentiated sarcomatous component. This article describes three cases of dedifferentiated chondrosarcomas: two with bone localization and one with laryngeal cartilaginous localization presenting a rare dedifferentiation component, either epithelial or rhabdomyosarcomatous, which may pose a diagnostic challenge, particularly in micro-biopsy samples. The mechanism of dedifferentiation is still poorly understood, and the origin of the dedifferentiated component remains controversial., Competing Interests: Déclaration de liens d’intérêts Les auteurs déclarent ne pas avoir de liens d’intérêts., (Copyright © 2025 Elsevier Masson SAS. All rights reserved.)

We report the case of a 10-year-old child with bilateral mandibular localization of a central giant cell granuloma occurring in the setting of Noonan syndrome. The histological appearance was classic with two intermigled components, one fibrous with non-atypical mononuclear cells, the other consisting of numerous osteoclast-like giant cells. This aspect is similar to that observed in the brown tumor as well as that of cherubism, which can also give multiple bone lesions. We will discuss the other lesions to consider in case of benign giant cell bone lesions affecting the jawbones, sometimes multiple and part of which falls within the scope of RASopathies., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Bone tissue can be involved by primitive or metastatic tumors and requires a specific processing both at the department of pathology and during multidisciplinary meetings. The development of fine-needle percutaneous biopsies and of molecular techniques in bone tumor pathology requires a specific management. Moreover, decalcification of samples is crucial but can be deleterious if not controlled or not appropriate. The aim of this review is to provide recommendations for management and decalcification of bone tumor samples., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

The group of notochordal tumors consists of the benign notochordal cell tumor and the conventional, dedifferentiated and poorly differentiated chordomas in the fifth edition of the WHO classification of bone and soft tissue tumors. This update covers recent advances in the knowledge of the histogenesis and biology of these tumors and their implications in terms of diagnosis, prognosis assessment and therapeutic management., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Giant cell tumors of bone (GCTs) are rare mesenchymal tumors classified as intermediate in the WHO 2020 classification, i.e. neither completely benign nor definitely malignant, due to recurrence (frequent) and pulmonary metastases (rare). They involve the end of long bones as well as the axial bones of mature skeletons. They are made of mononuclear stromal tumor cells of (pre-) osteoblastic phenotype, mononuclear cells of the monocyte-macrophage lineage and osteoclast-like multinuclear giant cells responsible for tumor osteolysis. In 95% of cases, the stromal cells have a specific mutation in the H3F3A gene which encodes histone H3.3. The mutated H3.3 G34W protein (90% of cases) can be easily detected by immunohistochemistry, even on small samples. Many tumors or bone pseudotumors contain osteoclast-like giant cells, cells of the bone microenvironment, and should not be confused with GCT: mainly brown tumor of hyperparathyroidism, aneurysmal bone cyst, chondroblastoma, non-ossifying fibroma and central giant cell granuloma., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Myxoglobulosis is a rare macroscopic form (<1%) of appendiceal mucocele characterized by opaque mucin beads. This entity, still unknown in clinical practice, can only be confirmed by anatomopathological examination. Many histological diagnoses that may impact the prognosis of patients should be discussed in the presence of myxoglobulosis, including neoplastic causes. We report the rare case of myxoglobulosis, whose histopathological management concluded the diagnosis of low-grade appendicular mucinous neoplasm., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

The infiltration by numerous osteoclastic giant cells is a frequent finding in bone tumors and pseudo-tumors. Pathologists must integrate clinical and radiological data to achieve a correct diagnosis in bone pathology. Benign giant-cell rich lesions of bone encompass giant cell tumor of bone, aneurysmal bone cyst, chondroblastoma, brown tumor and fibrous cortical defect/non-ossifying fibroma. Amongst malignant neoplasms, variants of conventional osteosarcoma, undifferentiated pleomorphic sarcoma, leiomyosarcoma and bone metastasis must be discussed. Recently, new diagnostic markers, antibodies for immuno-histochemistry and genetic markers, have been developed and are helpful to diagnose such lesions., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.)

Malignant transformation of a fibrous dysplasia into an osteosarcoma is very rare. We report the case of an 84-year-old man with telangiectatic osteosarcoma of the upper femur arising in a previous fibrous dysplasia also known as liposclerosing myxofibrous tumor. The tumor was expressing the epithelial membrane antigen. This is the first described case of a malignant transformation into an osteosarcoma arising in a liposclerosing myxofibrous tumor. We discuss the main differential diagnosis with a review., (Copyright © 2012 Elsevier Masson SAS. All rights reserved.)

We present the case of an embryonal rhabdomyosarcoma of orbitary location with aberrant expression of epithelial markers in a 51-year-old female. The rhabdomyosarcoma is a rare tumor of soft tissues affecting mainly the child, but also exceptionally adults over 50. When it presents as a small round cells tumor, particularly in the region of head and neck, its differential diagnosis with several other poorly differentiated tumors may be difficult. Several cases of rhabdomyosarcoma with aberrant expression of epithelial markers have been reported in the literature. A large immunohistochemical panel is recommended by recent studies in order to avoid diagnostic errors. It includes large spectrum cytokeratins, desmin, neuroendocrine, melanocytic and lymphoid markers. Our observation confirms the importance of conducting this immunohistochemical panel including desmin in the context of a poorly differentiated tumor of the head and neck region. It should be performed whatever the age of the patient and even if the tumor expresses epithelial markers., (Copyright © 2012 Elsevier Masson SAS. All rights reserved.)

The survival of osteosarcoma and Ewing family tumours has been improved by the introduction of neoadjuvant chemotherapy. The response to preoperative chemotherapy is evaluated on the microscopic analysis of the surgical resection, by the percentage of tumour necrosis according to the Huvos and Rosen's grading. It remains the only reliable prognostic factor for patients and is used to guide the choice of post-operative chemotherapy. The macroscopic and microscopic management of the surgical resection (cf. supra) is essential and is the subject of a specific protocol. Several studies have been conducted to identify news factors able to predict the response to chemotherapy, the tumour aggressiveness and its ability to develop metastases. Inhibitors of mTOR and/or regulators of the balance RANKL/OPG are promising therapeutics. The study's expression of these new factors could be performed on the biopsy and will offer new therapeutic strategy., (Copyright © 2011 Elsevier Masson SAS. All rights reserved.)

We report a case of PEComa (or perivascular epithelioid cell tumor) in an unusual articular localization in a 13-year-old boy. The tumor, of 4 cm in diameter, showed an infiltrative pattern and was composed of both epithelioid and spindle cells with clear to granular eosinophilic cytoplasm and some multinucleated giant cells. Focal nuclear pleomorphism was present and we found up to 2 mitotic figures /50 high power field. There was no necrosis. Immunohistochemistry showed HMB-45 and smooth muscle actin positivity. Ultrastructurally, premelanosomes were present. Some rare cases of PEComa were reported in the soft tissues. The immunohistological profile (HMB-45 and smooth muscle actin positivity and PS-100 negativity) is helpful to the diagnosis. The histological prognostic criteria of these tumors are not well established. We discuss here the differential diagnosis, notably clear cell sarcoma of soft tissue.

We present practical guidelines for the examination of orchidectomy specimens and propose a standardized worksheet for the pathology report of germinal tumors.

Chondroblastoma is one of the most well defined cartilaginous tumors of bone on imaging and pathological findings. However in practice, the pathologist is faced with diagnostic difficulties. The most recent features of the tumor are developed in the review: clinical findings, skeletal distribution, and above all, the results of the imaging study which has to be strictly correlated with histology for the diagnosis as well as for the differential diagnosis, location, osteolysis, matrix production, periosteal reactions, MRI studies. Histopathology of chondroblastoma is described: cellular component, architecture, and secondary changes. Usefulness of cytopathology is also stressed on smears or tumor imprints. Main findings of recent and various immunohistochemical stains are described and discussed as well. Ultrastructural and cytogenetic studies are summarized. Treatment, natural history, and prognosis of the tumor are developed. The three most important differential diagnoses are giant cell tumors, clear cell chondrosarcomas, and aneurysmal bone cysts.

We report the case of a prostatic phyllodes tumor in a 47-year-old man. It measured 6 cm and was composed of a glandular component with leaf-like architecture, lined with two cellular layers, and a moderately cellular stromal component, with no atypia and no mitosis. Basal cells were marked with high-molecular-weight cytokeratin antibody (34BE12) and stromal cells were marked with anti-vimentin and for some of them with CD34 antibodies. Prostatic phyllodes tumor is a rare lesion with uncertain prognosis. Total surgical removal is necessary because malignant transformation to high-grade sarcoma has been reported. In our case the development of the tumor at the posterior side of the prostate, the lack of PSA immunoreactivity and the presence of mucinous glands, sometimes "endocervical-like", could suggest an origin from embryonic mullerian remnants in the prostatic utricle rather than urogenital sinus.

We report two cases of pararenal angiomyolipomas, in two middle-aged women without tuberous sclerosis. Both tumors were made of muscular epithelioid cells without atypia, some of which were stained by HMB-45 antibody. The fibrous stroma contained numerous thick-walled blood vessels but no adipose component. The ultrastructural examination revealed that muscular epithelioid cells contained myofilaments and melanosomas. Because of their immunohistochemical and ultrastructural profiles, both tumors may be included in the family of lesions composed of perivascular epithelioid cells (PEC). This tumor type is considered as a particular variant of angiomyolipoma with predominant muscular epithelioid component. The immunohistochemical expression of progesterone and estrogen receptors by both tumors may suggest their hormonodependent character.

The renal medullary carcinoma is a rare tumor. We report a case in a black patient with sickle cell trait. The tumor was located in the lower pole of the left kidney. It had a tubular and microcystic architecture. It was composed of large eosinophilic cells with vesicular nuclei containing prominent nucleoli, in a desmoplastic and inflammatory stroma. By immunohistochemistry, the tumoral cells were positive for cytokeratin and Ulex europaeus lectin. Electron microscopy revealed small intracytoplasmic lumina with microvilli. The flow cytometric study showed DNA-multiploidy. The cytogenetic study revealed tetraploidy without structural abnormality. The renal medullary carcinoma is often reported in young black patients with sickle cell trait. Its microscopic, immunohistochemical and ultrastructural features favor its identification as a particular variety of Bellini duct carcinoma. Its link with sickle cell trait has to be defined.

Hyalinizing spindle cell tumor with giant rosettes is a slowly growing tumor with a risk of local recurrence in case of incomplete surgical excision that could be regarded as a distinctive type of low-grade fibroblastic tumor. We report a case involving the presacral area. This tumor was composed of areas of bland spindle cell proliferation with a fascicular pattern in a fibrous or myxoid stroma, intermixed with giant rosettes consisting of rounded cells surrounding a central collagen core. The tumor expressed vimentin, and, for cells comprising the rosettes, S-100 protein, NSE and CD-57. These latter cells exhibited ultrastructural features of Schwann cells, the tumoral cells of fascicular area exhibiting features of fibroblastic cells. Flow cytometry showed DNA-aneuploidy and a very low S-phase fraction. This tumor appeared to be composed of two cellular components, fibroblastic and Schwann cells, located, at the opposite of neurofibroma, in two distinct areas.

We report a case of Castleman's disease in a 65-year-old female, revealed by a renal tumor associated with inter-aortico-cava adenopathies and renal chromophobe cell carcinoma. This observation points to the difficulties in differentiating local Castleman's disease, which may be cured by surgical excision, from multicentric disease associated with a dysimmune syndrome of uncertain prognosis. The association of multicentric Castleman's disease with a carcinoma has rarely been described. It could be the emergence of a neoplasia in a context of dysimmunity or Castleman's disease might be related to the production of interleukin 6 by a renal carcinoma.

We report a case of clear cell sarcoma of kidney (CCSK), in a young adult. This highly malignant renal tumor usually arises in children of one or two year old and represents 4% of renal tumors. The aggressivity of this tumor and its affinity to give bone metastasis imply to recognize it in order to institute appropriate chemotherapy.

We report nine cases of anorectal melanoma illustrating the histopathological features of these tumors. In all cases, the diagnosis was made at symptomatic stage. Eight patients were treated by surgical procedure which consisted of abdominal perineal resection or local excision. The tumor was either monomorphous, composed of epithelioid or spindle cells, or polymorphous containing both cell types. One case was characterized by small cells resembling plasma cells. Pigmentation was inconstant. Tumor cells were marked by antibodies directed against the S100 protein (9 cases/9), HMB45 (4 cases/7) and vimentin (5 cases/7). As suggested by these cases, the diagnosis of melanoma should be systematically kept in mind in case of an anorectal tumor with unusual histopathological features.