Atypical fibroxanthoma/pleomorphic dermal sarcoma of the scalp with aberrant expression of HMB-45: a pitfall in dermatopathology

Pleomorphic Dermal Sarcoma

Pleomorphic dermal sarcoma (PDS) is a rare cutaneous/subcutaneous neoplasm of purported mesenchymal differentiation that exists along a clinicopathologic spectrum with atypical fibroxanthoma (AFX). While PDS and AFX share histopathologic and immunohistochemical features, PDS exhibits deeper tissue invasion and has a higher rate of metastasis and local recurrence than AFX. Given its aggressive clinical course, early recognition and clinical management of PDS are essential for optimizing patient outcomes. This review aims to provide a brief overview of the clinicopathologic and molecular features, prognosis, and treatment of PDS.

Dedifferentiated and undifferentiated melanomas: a practical approach to a challenging diagnosis

Dedifferentiation, defined as the loss of cellular features of terminal differentiation resulting in a more primitive, unspecialized phenotype, is a rare phenomenon in melanoma and more commonly observed in the metastatic setting than in primary melanomas. The diagnosis of dedifferentiated melanoma poses a significant challenge, and the tumors need to be carefully sampled and worked up to identify any residual morphologic, immunohistochemical, or molecular evidence of their melanocytic lineage. This article reviews our current knowledge of the clinical, histopathological, immunohistochemical, and molecular features of these rare tumors and provides a practical diagnostic approach and discussion of the relevant differential diagnoses and associated diagnostic pitfalls.

Primary Undifferentiated/Dedifferentiated Cutaneous Melanomas-A Review on Histological, Immunohistochemical, and Molecular Features with Emphasis on Prognosis and Treatment

Diagnosing cutaneous melanoma is usually straightforward based on these malignancies' histopathological and immunohistochemical features. Nevertheless, melanomas can imitate various other neoplasms, sometimes lacking the expression of conventional melanocytic markers and expressing non-melanocytic ones. Furthermore, divergent differentiation is more often encountered in metastatic melanomas and is still poorly described in primary cutaneous melanomas, and little is known about these patients' prognosis and therapeutic approach. Therefore, we reviewed the literature on undifferentiated/dedifferentiated cutaneous melanomas, and we discuss the histological, immunohistochemical, and molecular profiles of undifferentiated/dedifferentiated cutaneous melanomas to understand these peculiar lesions better and improve their diagnostic algorithm. In addition to this, we also discuss how different genetic mutations may influence prognosis and become potential therapeutic targets.