Non-melanoma skin cancer
Basal cell carcinoma and squamous cell carcinoma both arise from UV-driven DNA damage to epidermal keratinocytes, but their different cell of origin means BCC grows slowly and almost never metastasises while SCC can invade and spread, a distinction that dictates how urgently each is referred.
First principles
Both cancers start with UV damage to keratinocytes, but at different depths
Cumulative ultraviolet exposure causes mutations in epidermal keratinocytes. Basal cell carcinoma arises from basal-layer stem cells, commonly through mutations activating the hedgehog signalling pathway. Squamous cell carcinoma arises from more superficial, actively differentiating keratinocytes, typically progressing through a visible pre-malignant stage: actinic keratosis, then squamous cell carcinoma in situ (Bowen's disease), before becoming invasive. This difference in cell of origin is what makes the two cancers behave so differently.
Educational content pending clinical review. Not medical advice.