Basal cell carcinomas (BCC) and melanoma (MM) are common cutaneous malignancies. However, the development of a basomelanocytic tumour which simultaneously includes elements of both MM and BCC is extremely rare. We present the case of an 84 year old male who presented with a non-pigmented, non-ulcerated pink nodule of his left upper back.
Excisional biopsy showed a malignant neoplasm centered in the dermis without melanocytic proliferation in the epidermis or at the dermoepidermal junction. The tumour nodule was composed of two morphologically distinct, but spatially intermingled populations of tumour cells. Immunohistochemistry confirmed the presence of a tumour cell population that demonstrates epithelial differentiation, and another tumour cell population that demonstrates melanocytic differentiation. The absence of melanoma in situ, and the spatially intermingled tumour cell populations suggested a tumour with divergent differentiation. Based on the histological features, a collision (basal cell carcinoma and melanoma) tumour was unlikely. A scar re-excision with 20mm surgical margins and sentinel lymph node biopsies from the left upper back, left neck and left axilla were performed.
Treatment recommendations differ between various centres with some preferring treatment of basomelanocytic tumours as per melanoma in situ with conservative margins, while others recommend a wider excision and consideration for sentinel lymph node biopsy staging.1-4 The authors consider a wider local excision and possible sentinel lymph node biopsy advisable; however, firm recommendations cannot be provided until more research is available.