system
Given the following post, respond as if you're commenting on Reddit:
human
Why does basal cell carcinoma so rarely metastasize?

Biochemically/genetically speaking.
gpt
I believe you are implocitly comparing BCC to melanoma - they are derived from different cells and the epithelial cells are much more terminally differentiated and more committed than melanocytes which easily restore their mobility which enables metastasis.

Short answer is that melanocytes migrate during embryogenesis and provide pigmentation (defects in this process are observed in many animals where they are unpigmented at terminal sites far from the neural tube origin like peripheral limbs - white socks and ventral surfaces in cats and dogs). Because melanocytes migrate in to the highly differentiated epithelial tissue, these melanocytes are then the most easily transformed cells when it comes to oncogenic mutations. Because they migrated through other tissues they are also less dependent on the local environments.

A cancer cell needs to acquire mutations that revert its differentiation so it can move, adhere to other sites, ignore local signals, and replicate independently. The more stem-like a cell to begin with the more easily it is able to acquire this phenotype through mutation. In their terminally differentiated state melanocytes are much more stem-like than basal epithelial cells.