Do You Have to Have a Biopsy Before Mohs Surgery?

Prior to performing surgery for a skin cancer using Mohs micrographic surgery, the diagnosis should be confirmed with a biopsy, otherwise, you might undergo unnecessary surgery, with risks that are not warranted. The biopsy could be a frozen biopsy and if the results prove there to be a skin cancer, then the Mohs surgery could be done. Usually, a biopsy is done in a standard fashion and sent to a laboratory for permanent section analysis (not frozen). Then when the result returns days later, the surgery is scheduled if needed.

A biopsy is performed to establish a diagnosis of skin cancer.  Mohs surgery is best applied for well differentiated skin cancers (BCCA, SCCA) in sensitive anatomic areas. 

Yes.  Mohs' surgery is a technique used to evaluate the margins only, it does not diagnose skin cancer.  Therefore prior to Mohs' a biopsy must ALWAYS be done, although can be done immediately prior to Mohs'.