Mohs surgery

Mohs surgery, developed in 1938 by general surgeon Frederic E. Mohs, is microscopically controlled surgery used to treat both common and rare types of skin cancer. During the surgery, after each removal of tissue and while the patient waits, the tissue is examined for cancer cells. That examination dictates the decision for additional tissue removal. Mohs surgery is the gold standard method for obtaining complete margin control during removal of a skin cancer (complete circumferential peripheral and deep margin assessment using frozen section histology. This method allows for the removal of skin cancer with a very narrow surgical margin and a high cure rate.

The cure rate with Mohs surgery cited by most studies is between 97% and 99.8% for primary basal-cell carcinoma, the most common type of skin cancer. Mohs procedure is also used for squamous cell carcinoma, but with a lower cure rate. Recurrent basal-cell cancer has a lower cure rate with Mohs surgery, more in the range of 94%. It has been used in the removal of melanoma-in-situ (cure rate 77% to 98% depending on surgeon), and certain types of melanoma (cure rate 52%).

Other indications for Mohs surgery include dermatofibrosarcoma protuberans, keratoacanthoma, spindle cell tumors, sebaceous carcinomas, microcystic adnexal carcinoma, merkel cell carcinoma, Paget's disease of the breast, atypical fibroxanthoma, and leiomyosarcoma. Because the Mohs procedure is micrographically controlled, it provides precise removal of the cancerous tissue, while healthy tissue is spared. Mohs surgery can also be more cost effective than other surgical methods, when considering the cost of surgical removal and separate histopathological analysis. However, Mohs surgery should be reserved for the treatment of skin cancers in anatomic areas where tissue preservation is of utmost importance (face, neck, hands, lower legs, feet, genitals).

Skin cancer can be categorized into two groups: melanoma, which is considered more severe, and nonmelanoma skin cancer which includes basal cell carcinoma and cutaneous squamous cell carcinoma.

Mohs micrographic surgery is used for high-risk nonmelanoma skin cancers located in cosmetically critical or sensitive areas like the face, ears, scalp, neck, genitalia, hands and feet where tissue conservation is of utmost importance. It is also indicated when the tumor is recurrent, aggressive, large, or painful which tells us there is invasion of the nerve or vasculature.

Some cases of melanoma, such as early, surface-level melanoma (lentigo maligna) or thin invasive melanoma, can be treated with Mohs surgery. This is especially considered in areas where tissue sparing is essential. In these cases special immunohistochemical staining is used to visualize the melanoma cells, evaluate the margins, and ensure the cancer has been completely removed. More evidence today is linking Mohs surgery with lower recurrence rates of melanoma in these cases. 

This approach is also used in treating rare skin malignancies like dermatofibrosarcoma protuberans and a few adnexal tumors (tumors arising from hair follicles, sebaceous glands or sweat glands) where margin clearance is essential.

In summary, the Mohs micrographic surgery criteria are as follows: