“Biphasic” in medical terminology means: having two phases, parts, aspects, or stages. In dermatopathology, many conditions are described as having a biphasic pattern. However, this term represents three different categories.

The first category of lesions described as having a biphasic pattern represents certain tumors showing two distinct morphological areas. For example, one area shows a hemangiopericytomatous morphology with ramifying vascular spaces with stag horn appearance surrounded with tightly packed spindle cells with round to oval nuclei and the other area shows a different morphology which can be in the form of short fascicles of plump spindle cells with esinophilic cytoplasm in myofibromatosis (or myopericytoma) or epithelioid cell component forming glandular structures of variable sizes in biphasic synovial sarcoma.

Another category representing the biphasic pattern is when we find a collision of two different tumors in a single lesion. One can see the morphology of two different adnexal tumors, an adnexal and epithelial tumor, an epithelial and melanocytic (squamomelanocytic) tumor or an adnexal and melanocytic (basomelanocytic) tumor.

Finally, the word biphasic is also used to describe the growth pattern of melanoma as it grows in both a radial phase and a vertical phase.