How accurate is a skin biopsy?

Skin biopsy: This really depends on what is being biopsied. For a "nodule" or "bump," to rule out cancer, a biopsy is usually likely to give a very accurate diagnosis, although some early forms of cancer can be difficult. Biopsies of "rashes" are more tricky. Sometimes the histology is classical, and a very specific diagnosis can be made. But sometimes the biopsy has a non-specific appearance.