Primary cutaneous cancers are classified on the basis of their cell of origin within the skin (Table 44-1). Skin cancers are most commonly derived from keratinocytes (e.g., squamous cell carcinoma) or melanocytes (e.g., malignant melanoma), which are normal components of the epidermis. Less commonly, they arise from other cells within the epidermis, dermis, or subcutis.
| Table 44-1. Classification of Cutaneous Malignancies |
| | MALIGNANCY | | CELL OF ORIGIN |
| | Premalignancies (in situ) | | |
| | Actinic keratosis | | Keratinocyte |
| | Squamous cell carcinoma in situ (Bowen’s disease) | | Keratinocyte |
| | Malignant melanoma in situ | | Melanocyte |
| | Lentigo maligna (Hutchinson’s freckle) | | Melanocyte |
| | Common Cutaneous Malignancies | | |
| | Basal cell carcinoma | | Follicular keratinocyte origin (probable) |
| | Squamous cell carcinoma | | Epidermal keratinocyte |
| | Keratoacanthoma | | Follicular keratinocyte |
| | Melanomas | | |
| | Malignant melanoma | | Melanocyte |
| | Lentigo maligna melanoma | | Melanocyte |
| | Uncommon Cutaneous Epithelial Malignancies | | |
| | Sweat gland carcinoma (numerous variants) | | Apocrine or eccrine sweat gland/duct |
| | Follicular carcinomas (several variants) | | Follicular epithelial cells |
| | Extramammary Paget’s disease | | Modified keratinocytes (Toker cell) |
| | Merkel cell carcinoma | | Neuroendocrine cell |
| | Cutaneous Mesenchymal Malignancies | | |
| | Atypical fibroxanthoma | | Fibroblast |
| | Dermatofibrosarcoma protuberans | | CD34+ dermal dendrocyte |
| | Fibrosarcoma | | Fibroblast |
| | Angiosarcoma | | Endothelial cell |
| | Kaposi’s sarcoma | | Endothelial cell |
| | Hemangiopericytoma | | Pericyte |
| | Malignant peripheral nerve sheath tumors | | Schwann cells |
| | Liposarcoma | | Lipocyte |
