Mohs Surgery: What to Expect on the Day of Surgery

Mohs surgery is typically performed as an outpatient procedure in a medical office or surgery clinic where there is an on-site lab. The procedure can take several hours as it is done in stages. Find out what to expect on the day of your surgery.

Before the Surgery

Since the surgery is performed under local anesthesia only, you won't have to make too many preparations. For most surgeries—even outpatient procedures—healthcare providers give you instructions on what medications to avoid, and whether to refrain from eating or drinking for a number of hours before surgery in the days before the procedure.

You may be asked to change into a hospital gown, but you may also be able to remain in your regular clothes, depending on the location of the area to be treated. Be sure to wear clothing that allows easy access to area of concern.

Your healthcare provider will have already performed a number of diagnostic tests before the day of surgery, but may want to get some basic information like blood pressure, heart rate, temperature, and possibly blood glucose before starting the procedure.

During the Surgery

Mohs surgery is performed in one day as an outpatient or ambulatory procedure, but takes place in stages.

Stage 1: Re-Examination and Preparation

When you arrive on the day of your procedure, you will be brought into a procedure area. This is when you may need to change into a hospital gown, depending on the location of the skin cancer.

Your surgeon will take a look at your biopsy site and mark it with a surgical pen. At this point, you will be draped in a sterile surgical drape and positioned in a way that optimizes the surgeon's access to the affected site. You will be awake throughout the procedure, but local anesthesia will be used so you don't feel any pain.

Stage 2: Removal of the Top Layer

The first incision will be minor, with your surgeon removing only the top layer of the affected area. The entire tumor may not be visible to the surgeon, with roots that extend far below the skin's surface.

After the initial surface removal, the surgical site will be covered. You will get a break while the first sample is sent to a special Mohs lab for immediate testing.

Stage 3: Lab Testing and Microscopic Examination

The tissue that was removed will be divided into quarters and marked on a corresponding pictorial map. The tissue sample will then be sent for frozen tissue processing, which involves placing smaller pieces of the tissue marked with dye on slides and examining them under a microscope. The results of this analysis will guide the remainder of the tumor removal.

Stage 4: Second Layer Removal

Once the first layer of the affected tissue is analyzed, your surgeon will let you know if additional tissue must be removed. The lab analysis notes where cancerous cells remain, and on how much or the surgical area using the map created by the surgeon.

Based on the map created by the surgeon and the lab result, your surgeon will inject more local anesthesia into the affected area, removing only the areas where cancer remains. As this next layer is removed, your surgeon will once again remove a small layer of tissue, create a map, and send the tissue out for testing.

Stage 5: Additional Analysis and Removal

The previous steps will be completed as many times as necessary, with the surgeon removing layers and the lab analyzing those layers for remaining cancer cells until there is no evidence of any cancer left in the affected area. In most cases, narrow margins of just 1 to 2 millimeters (mm) around the tumor are removed.

Stage 6: Wound Closure

Once your surgeon is certain the affected area is clear of cancer cells, the wound left behind from the tissue removal will be closed for later repair, or repaired immediately by your surgeon.

After the Surgery

Your surgeon will determine the best method for reconstruction once they are sure the tumor margins are clear of any more cancer cells. Depending on the location and size of the tumor, it may be repaired right away, or your surgeon may have you follow up with a plastic or reconstructive surgeon some time after our surgery.

If the repair happens on a different day, your surgeon will cover the wound or stitch it closed. Larger tumor removal might mean the area has to be repaired with a skin graft or local flap.

You will be able to go home when the procedure is complete regardless of your reconstruction plans. The entire surgery can take several hours, but the minimal disruption of surrounding tissue and high success rate for complete cancer removal is the end benefit for this procedure.

Your healthcare provider will give you clear instructions on wound care and follow up appointments before you go home.

A Word From Verywell

Mohs surgery is an exact technique that is highly effective in completely removing skin cancer that is typically prone to returning, or has returned after other procedures in the past. This outpatient surgery can take many hours, but is still completed within a day. The payoff of this procedure is minimal tissue loss with high curative rates.