In the first stage of the Mohs skin cancer surgery, a local anesthetic is injected in the area that is to be treated after it has been cleaned and the potentially cancerous area marked. Any visible skin cancer is removed and then a thin layer of additional tissue is removed. This part of the surgery is usually quick, only lasting for several minutes.
A diagram is then made of the removed tissue specimen after it has been cut into sections and stained. The tissue is frozen using a cryostat and thin slices are removed from the edge of the specimen and from the undersurface. Each of these slices of tissue are put on slides and stained. This part of the procedure takes the most time and may take over one hour to complete.