The removal of skin cancer is a common medical procedure, and the surgical technique chosen affects both the cure rate and the cosmetic outcome. The two primary methods for eliminating basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are standard excisional surgery and Mohs micrographic surgery. The core difference lies in how the surgical margins—the edges of the removed tissue—are handled and analyzed. Standard excision removes the tumor with a fixed margin of surrounding tissue, while the Mohs technique removes the cancer in thin layers, allowing for immediate, microscopic margin control.
How Standard Excisional Surgery Works
Standard excisional surgery involves removing the visible skin cancer along with a predetermined, fixed border of healthy skin. This fixed margin is typically 2 to 4 millimeters of tissue surrounding the tumor, chosen to maximize the chance of complete removal in a single procedure. The surgical site is then closed with stitches, and the entire tissue specimen is sent to an external pathology laboratory for analysis.
At the lab, the tissue is processed using vertical sectioning, often called “bread-loafing.” This technique allows for the examination of only a small portion of the surgical margin, usually about one percent of the total edge. Because this process requires chemical fixation and specialized preparation, the patient must wait several days to over a week for the pathologist’s report. If the margins are reported as positive for cancer, the patient must return for a second or third procedure to remove more tissue, resulting in treatment delay and a larger final scar.
How Mohs Micrographic Surgery Works
Mohs micrographic surgery is a specialized technique performed by a surgeon who also acts as the pathologist. The procedure begins with removing the visible tumor followed by a thin layer of surrounding tissue, typically using a 1 to 2 millimeter margin. This tissue layer is immediately taken to an on-site laboratory, where it is rapidly frozen using a cryostat and horizontally sectioned.
The horizontal sectioning allows the surgeon to examine 100% of the peripheral and deep surgical margins under a microscope in real time while the patient waits. If cancer cells are detected, the precise location is mapped. The surgeon then removes an additional, ultra-thin layer of tissue only from the exact spot where the cancer remained. This staged process repeats until a clear, cancer-free margin is confirmed, ensuring maximum tumor removal with minimum tissue loss.
Comparing Cure Rates and Tissue Preservation
The difference in margin analysis translates into superior outcomes for Mohs surgery in specific cancer types and scenarios. Mohs surgery achieves higher five-year cure rates for common non-melanoma skin cancers, especially those that are aggressive or recurrent. For primary BCC, Mohs offers a cure rate of approximately 99%, compared to about 90% for standard excision.
This advantage is more pronounced for recurrent tumors. Mohs maintains a cure rate near 94% for BCC and 90% for SCC, contrasting with rates as low as 83% and 77% respectively for standard excision. The ability of Mohs to microscopically check the entire margin ensures fewer cancer cells are left behind, leading to a much lower recurrence rate (one to three percent) compared to standard excision (five to ten percent). The precise, layer-by-layer removal of only cancerous tissue is known as tissue sparing, which preserves the largest amount of healthy skin, resulting in smaller, less noticeable scars.
Determining Which Procedure Is Appropriate
The choice between Mohs surgery and standard excision is determined by the characteristics and location of the skin cancer. Mohs surgery is the preferred option for tumors located in areas where preserving every millimeter of healthy tissue is a priority for functional or cosmetic reasons.
Indications for Mohs Surgery
Mohs is recommended for cancers that are large, have poorly defined edges, exhibit aggressive features, or have recurred after previous treatment. It is also preferred for sensitive areas, including the face, ears, nose, lips, scalp, hands, feet, and genitals.
Indications for Standard Excision
Standard excisional surgery is often the appropriate treatment for smaller, well-defined, non-aggressive cancers situated on the trunk, arms, or legs. In these areas, the cosmetic outcome is less of a concern, and the added time and complexity of the Mohs procedure are not required. The final decision is individualized, based on the tumor’s size, type, location, and the patient’s overall health and aesthetic goals.