Primary rhabdoid melanoma with clonal recurrence

PRAME Expression as Helpful Immunohistochemical Marker in Rhabdoid Melanoma

Background: Rhabdoid melanoma is a rare variant of malignant melanoma with characteristic cytomorphologic features. Due to the potential loss of conventional melanocytic markers, histopathologic diagnosis is often challenging. We hypothesize that immunostaining for PReferentially expressed Antigen in MElanoma (PRAME) might have the potential to uncover the melanocytic origin of these dedifferentiated tumors. Methods: Four cases of rhabdoid primary melanomas were assessed by immunohistochemistry for expression of PRAME and conventional melanocytic markers. Immunohistochemical expression patterns were analyzed in the rhabdoid primaries and, if available, associated metastases. Results: All four cases of rhabdoid primary melanomas showed a strong nuclear positivity for PRAME, while the expression of conventional melanocytic markers S100, MART-1, SOX-10 and HMB-45 was variable between the analyzed cases. Conclusions: In summary, we report four cases of rhabdoid primary melanoma with high to intermediate expression of PRAME despite the partial and variable loss of other melanocytic markers. Hence, PRAME might facilitate the recognition of this highly aggressive entity to avoid misdiagnosis due to histopathologic pitfalls.

Uncommon Histopathological Variants of Malignant Melanoma. Part 2

Despite new horizons opened by recent advances in molecular pathology, histological evaluation still remains the diagnostic gold standard regarding cutaneous melanocytic neoplasms. Several histological variants of melanoma have been described, and their knowledge is crucial for accurate diagnosis and classification of cases with unusual clinico-pathological features. Uncommon histological variants of melanoma have been described based on a broad constellation of features, including architectural pattern, stromal alterations, cytological attributes, and other morphological properties. This review is aimed at providing an extensive discussion of unusual but distinctive histopathological variants of melanoma.

Primary Vaginal Melanoma With Rhabdoid Features: A Case Report and Literature Review

Primary vaginal melanoma is a rare mucosal neoplasm, which is more aggressive than cutaneous melanoma. Information regarding its morphologic patterns is limited. In particular, the rhabdoid phenotype, mostly observed in metastatic or recurrent cutaneous melanomas, has yet to be reported at this anatomic location. Hence, a potential diagnostic difficulty may arise because of the inability to recognize this unusual histologic variant and its immunohistochemical aberrance. In this report, we describe the case of a primary vaginal melanoma in a 62-year-old woman, who exhibited both rhabdoid and small blue round cell morphologies, absence of S100 protein, and aberrant expression of desmin, CD56, and FLI-1. This report can facilitate the task of expanding the morphologic spectrum of vaginal melanoma, and prevent misdiagnosis and inadequate medical treatment.

Primary Amelanotic Rhabdoid Melanoma: A Case Report with Review of the Literature

Primary rhabdoid melanoma (PRM) is a rare variant of melanoma. Herein, we describe a case of primary amelanotic rhabdoid melanoma and review the clinicopathological features of previously reported cases of PRMs. A 63-year-old Japanese man presented with a nonpigmented red granular tumor without peripheral pigmented macules on the left heel measuring 21 × 18 mm in size. Light microscopic examination revealed a tumor mass composed entirely of polygonal neoplastic cells resembling pulmonary alveoli. Tumor cells were also discohesive with bizarre nuclei, prominent nucleoli and large hyaline cytoplasmic inclusions. No melanin pigment was present. Tumor cells were strongly and diffusely positive for S-100, MART-1, HMB-45 and vimentin, while negative for desmin, αSMA and synaptophysin. According to previous reviews, PRM tends to be amelanotic and nodular. S-100 protein and vimentin stained in all cases contrary to low stainability for HMB-45, which was, by contrast, positive in our case. Prognosis of PRM remains controversial due to the very rare occurrence of this tumor and the small number of confirmed cases that have been reported. Recognition of this rare entity is important in clinical practice even for skillful dermatologists to avoid misdiagnosis with the other tumors and to determinate the subsequent treatment principles.

Primary sinonasal mucosal melanoma with aberrant diffuse and strong desmin reactivity: a potential diagnostic pitfall!

The broad morphologic spectrum, inherent immunophenotypic heterogeneity of malignant melanoma and its rarity in the sinonasal tract are major challenges in eliciting the correct diagnosis, which may lead to misclassification and inadequate medical management. Herein, we describe a single case of a 70 year-old male with sinonasal mucosal melanoma, exhibiting varying histologic phenotypes including small round blue cell morphology, epithelioid and focal rhabdoid morphology and strong, diffuse desmin immunoreactivity. These constellation of features initially prompted the diagnosis of rhabdomyosarcoma. The differential diagnosis in this anatomic area includes other malignant small round blue cell tumors of the sinonasal mucosa such as rhabdomyosarcoma, olfactory neuroblastoma, sinonasal undifferentiated carcinoma, and lymphoma. We reviewed precedent literature and further discuss the potential pitfalls to which pathologists may be prone.

Primary malignant rhabdoid melanoma

Melanoma with rhabdoid features is an uncommon variant of malignant melanoma. Here, we describe a rare case of primary rhabdoid malignant melanoma. A 54-year-old man presented with a black tumor measuring 3×4 cm on the right forearm. Histologic sections showed a tumor mass with rhabdoid features composed entirely of polygonal neoplastic cells with eccentric nuclei, prominent nucleoli, and large hyaline cytoplasmic inclusions. The tumor cells were immunoreactive with HMB-45, S100, Fontana-Masson silver and vimentin, and negative for smooth muscle actin, CD68, CD34, CD99, synaptophysin, desmin, and PAS. The differential diagnosis for this tumor included malignant peripheral nerve sheath tumor, malignant peripheral neuroectodermal tumor and rhabdomyosarcoma. The patient was treated with a wide excision and a local skin graft. The excised tumor was entirely composed of rhabdoid tumor cells. No recurrence or metastasis was evident 4 months after removal. This article is relevant to rare cases of primary malignant melanomas showing rhabdoid tumor cells over the entire excised lesion.

Clues to the diagnosis of atypical melanocytic lesions

This review, based on a lecture given at the 2009 Update in Dermatopathology meeting held at the Institute of Dermatology (London, UK), discusses the problem of misdiagnosing atypical benign melanocytic lesions as melanoma and the alternative problem of interpreting naevoid melanoma as a banal naevus. Consequences are considered. Brief consideration of a range of other melanoma variants that may be a source of diagnostic difficulty is also included.