Skin biopsy is a diagnostic test in which a small piece of tissue is removed, under local anesthesia, from a lesion that’s suspected of being malignant or from another dermatosis.

One of three techniques may be used: shave biopsy, punch biopsy, or excisional biopsy. Shave biopsy cuts the lesion above the skin line, which allows further biopsy of the site. Punch biopsy removes an oval or round core from the center of the lesion. Excisional biopsy removes the entire lesion and is indicated for rapidly expanding lesions, malignant or dysplastic tissue, ensuring clear margins of skin surrounding a lesion (when necessary), examining the border of a lesion surrounding normal skin, and sclerotic, bullous, or atrophic lesions.

Lesions suspected of being malignant usually have changed color, size, or appearance or have failed to heal properly. (See The ABCDEs of malignant melanoma.) Fully developed lesions should be selected for biopsy whenever possible because they provide more diagnostic information than lesions that are either resolving or in an early stage of development. For example, if the skin shows blisters, the biopsy should include the most mature ones.

Normal skin consists of squamous epithelium (epidermis) and fibrous connective tissue (dermis). Benign growths include cysts, seborrheic keratoses, warts, pigmented nevi (moles), keloids, dermatofibromas, and neurofibromas. Malignant tumors include dysplastic nevi, basal cell carcinoma, squamous cell carcinoma, and malignant melanoma.