• Dr. Danny Guo

Mohs Micrographic Surgery

Skin cancer is very common in North America and if caught early, it can usually be treated with surgical removal.


There are two main forms of skin cancer surgery: wide local excision and Mohs micrographic surgery.


Wide local excision is the most common and more readily available method where the surgeon identifies the tumor’s border and adds a margin based on the type of tumor. This is done because skin cancers often spread in the skin like roots, and what we see with the naked eye is usually not the whole picture. By adding predesignated margins based on the tumor type, surgeons are able to optimize the surgery’s cure rate. While the cure rate varies based on tumor type, it is usually 95% for basal cell carcinoma, (the most common form of skin cancer.) After removal, the tumor is sent to the pathology lab for confirmation - a process that can take several weeks to confirm if all of the tumor has been removed.


Mohs micrographic surgery is different from wide local excisions in several ways. Namely, that it is a multi-staged procedure. Instead of removing the tumor with a clinical margin, the tumor is removed with little to no margins. It is then processed immediately to determine whether there is any tumor left in the patient. If there is, the surgeon will then excise another small piece where the tumor remains and have it processed immediately. This process is repeated until the cancer is completely removed, and typically yields a cure rate of 99%.


There are two primary benefits of Mohs surgery. Since we are checking as we cut, we maximize the chance of completely removing the tumor. As we are removing only what we need, we minimize the amount of skin removed - thus optimizing cosmetic outcomes. These two benefits of Mohs surgery combine to make it the gold standard for most skin cancer treatment.


While Mohs surgery has amazing benefits over the traditional wide local excision, it has a significant drawback. As there are less than 30 Mohs surgeons in Canada, wait times are longer. It is important for the referring doctors and patients to decide together which method of treatment is the most appropriate and practical for each case.