Collision tumors are defined as two histologically different tumor types that arise at the same anatomical location. According to the literature review performed, there are reports of 27 cases of collision tumors involving lentigo maligna melanoma (LMM) in-situ and basal cell carcinoma (BCC). In the absence of melanocytic extension beyond the lamina propria of the BCC compartment, mixed tumors are considered as melanoma in-situ colonizing the BCC, rather than invasive melanomas. We report an uncommon case of collision of BCC with LMM, two primary skin tumors that are seen in patients with significant sunlight exposure. In our case, the patient is a 91-year-old male presented with a translucent plaque with areas of brown pigmentation on his left lateral canthus. He had a history of multiple BCCs, squamous cell carcinomas and an invasive melanoma of right cheek. Given the clinical impression of BCC, the lesion was curetted. Histological examination demonstrated melanoma in-situ heavily infiltrating the dermal nodules of BCC. Deposits of melanin pigment were scattered throughout the tumor. The BCC contained about 50% atypical melanocytes. Further immunohistochemical evaluation with melanocytic and epithelial markers (melanin A, SOX-10, pan-cytokeratin and p63) confirmed the diagnosis. An unequivocal independent invasive melanoma component was not identified in this material. The collision of BCC and LMM is very rare. However, given the sun-damaged changes promote both tumors, their development at the same site, although unexpected, can be explained. Since the prognosis of the two entities is independent, wider excision to exclude invasive malignant melanoma is indicated.
Melanoma in situ or superficial basal cell carcinoma?
