Biopsies can be divided into two broad groups, incisional and excisional. Excisional biopsy of a suspect skin lesion is ideal if the lesion is less than 1 cm, and good cosmetic and functional closure can be obtained. Incisional biopsy is useful in some cases where an excisional biopsy is not practical.
Incisional biopsy is particularly useful in basal cell carcinoma, where the tumour is homogeneous and a small fragment is generally representative of the entire lesion's histology. It is also very useful in the separation of lentigo maligna from the much more common benign lentigo simplex. A small shave biopsy of this flat brown patch on the face of an elderly individual can clearly differentiate whether the melanocytes are dysplastic or completely benign
Excisional biopsy is the preferred biopsy for most squamous carcinomas, particularly nodular squamous carcinomas. A nodular squamous carcinoma must be distinguished from a keratoacanthoma. Keratoacanthoma has a histology similar to but architecturally different from a squamous carcinoma. These self-limited lesions grow quickly over 8 to 12 weeks and then self remit. An incisional fragment of a keratoacanthoma can be misinterpreted as a squamous carcinoma and vice versa. The entire lesion should be submitted for histological review. That said, a large plaque of squamous carcinoma on for instance the forehead of an individual can be biopsied to define the diagnosis, and aid in the decision on appropriate therapy, whether surgical excision with flap closure and graft or radiation therapy.
It is important when biopsying a lesion that could be suspect for melanoma that the thickest part be biopsied to the full depth of the lesion and beyond. Prognosis depends upon the measured depth of invasion. If the thickest part is incompletely biopsied, and the base cauterized, it may not be possible to plan appropriate therapy because the depth of invasion will not be known. This is particularly a problem with "saucerization" as a method of biopsy.
It is important that the lesion not be shaved off the surface with cautery of the base, but rather deeply saucerized, if this technique is to be used. If there is any pigment at the base of the biopsy after the main tissue has been removed, that pigmented area should be submitted separately, and not cauterized from hemostasis.
Biopsy of melanoma and other skin cancers does not worsen prognosis.