Metastatic Mimics of Primary Cutaneous Lesions: Averting Diagnostic Pitfalls With Significant Repercussions

Cutaneous metastases by solid malignancies often signify advanced disease and portend severely limited survival. Appropriate diagnosis of these lesions is particularly hampered when they closely resemble primary cutaneous tumors. In this article, we present two diagnostically challenging cases of metastatic lesions to the scalp bearing striking histologic resemblance to primary cutaneous neoplasms. One case of a metastatic urothelial carcinoma showed epidermotropism as well as histologic and immunohistochemical features virtually indistinguishable from those of a poorly differentiated squamous cell carcinoma. Next generation sequencing was performed on both the primary urothelial carcinoma and scalp malignancy revealing an identical BRAF p. S467L somatic mutation, confirming the diagnosis. Another case of metastatic renal cell carcinoma showed clinical and histomorphologic features highly reminiscent of a pyogenic granuloma. These cases demonstrate the potential of metastatic lesions to assume a myriad array of innocuous disguises and underscore the vigilance required to avoid misdiagnosis. In addition, we highlight the emerging role of molecular strategies in resolving these problematic cases.