A neoplastic proliferation of basal cells in the epidermis (part of the skin) or other anatomic sites (most frequently the salivary glands). The basal cell neoplastic proliferation in the epidermis results in basal cell carcinomas. The basal cell neoplastic proliferation in the salivary glands can be benign, resulting in basal cell adenomas or malignant, resulting in basal cell adenocarcinomas. [ NCIT:C3784 ]