Collision Tumor Associated with Sarcomatoid Eccrine Porocarcinoma and Basal Cell Carcinoma.

A 'collision' tumor refers to the existence of two different neoplasms within the same tumor. Sometimes, the term 'biphasic tumor' is also used. However, a 'collision' tumor is defined as the occurrence of two neoplasms within proximity of each other yet maintaining distinctly defined, separate boundaries. In contrast, a 'biphasic' tumor demonstrates two or more phenotypically distinct neoplastic cell populations merging within the same space. Here, we report a case of collision tumor associated with sarcomatoid eccrine porocarcinoma and basal cell carcinoma arising in a 57-year-old male patient.