Abstract
Cutaneous BCC (BCC) has well established histopathology with a variety of known patterns, some of which have more frequent episodes of local recurrence. The variant patterns are not distinguished by cytological features and BCC is not segregated into “well, moderately or poorly differentiated” categories. Local recurrences are usually by direct extension. Vascular invasion is rare and satellite and distant metastases are exceptional. We describe a facial tumor in a 78-year-old man that first resembled an infiltrating basal cell carcinoma, had three recurrences in two years with each recurrence appearing after Mohs surgery. The successive recurrences had pathology of a poorly differentiated basaloid carcinoma that infiltrated as small, rounded cells with hyperchromatic nuclei forming cords, nests and occasional cribriform groups with prominent vascular and perineural invasion. The tumor cells were positive for cytokeratin 7, GATA3, cytokeratin 5/6, p63 and negative for MOC31, EMA, and for multiple sebaceous, neuroendocrine and melanocytic markers. Tumor sequencing identified high tumor mutation burden (81.1 mutations/MB) with mutations in PTCH1, TP53 and the TERT promoter, consistent with cutaneous basal cell carcinoma. The recurrences appeared as satellite metastases with prominent vascular and perineural invasion. Imaging studies showed no salivary gland or nodal neoplasia. This case and few in the literature suggest that there may be occasions when cutaneous basal cell carcinomas lose their typical microscopic appearance and immunohistochemical markers and show aggressive biology. Such tumors may in fact be “poorly differentiated” or “de-differentiated” basal cell carcinomas. Molecular analysis may help classify such tumors and show potential targetable mutations.
