Metastatic Basal Cell Carcinoma Molecular Ancillary Testing And Reappraisal Of Histopathology Within A Rare Entity

Objectives: Diagnosis of metastatic basal cell carcinoma (BCC) remains challenging, in part due to its rarity. With the advent of molecularly targeted therapies, recognition of this entity is more important than ever.Methods: We identified 11 cases of metastatic BCC over a 13-year period. We analyzed these tumors in conjunction with their respective primary tumors by histomorphologic, immunohistochemical, and molecular genetic analyses.Results: We identified three morphologic patterns of metastasis in BCC. The most common (seven cases) was characterized by completely typical features of BCC. Two cases showed marked squamous differentiation within BCC. The final two cases showed exclusively features of a poorly differentiated carcinoma. One of these was definitively classified by molecular analysis, as both the primary and metastatic tumors harbored the same inactivating PTCH1 mutation.Conclusions: This study illustrates multiple distinct morphologic patterns in metastatic BCC and highlights the utility of ancillary molecular testing for accurate diagnosis.