Mohs micrographic surgery, commonly referred to as Mohs surgery, is a specialized surgical procedure primarily used for the treatment of skin cancers, particularly those located in cosmetically and functionally critical areas, such as the face, ears, and eyelids. This technique, pioneered by Dr. Frederic Mohs in the 1930s, is unique in its ability to provide a high cure rate while minimizing tissue loss. The procedure combines precise surgical excision with immediate histologic evaluation, allowing for the complete removal of malignant skin tumors with minimal disruption to surrounding healthy tissue. The high success rates associated with Mohs surgery make it the treatment of choice for certain aggressive and recurrent skin cancers, particularly basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).

Mechanism of Mohs Surgery

The distinguishing feature of Mohs surgery lies in its approach to assessing surgical margins. Unlike traditional excision techniques, which remove a tumor and then send the excised tissue to a pathology lab for analysis, Mohs surgery uses a real-time, step-by-step process to evaluate the margins during the procedure itself. This is accomplished through the following steps:

• Marking and Tissue Removal: The surgeon begins by marking the area of the tumor to be excised. The specimen is removed with a small margin of surrounding healthy tissue. During this step, the surgeon ensures that the margins are well-delineated and accurately reflect the boundaries of the tumor.
• Processing and Sectioning: After the specimen is removed, it is immediately processed in a freezing microtome. This machine slices the tissue into thin sections that are then stained for examination under a microscope. The key innovation of Mohs surgery is that the surgeon, who is trained both in dermatologic surgery and histopathology, interprets the slides directly after the tissue is prepared. This allows for immediate assessment of the tumor margins.
• Margin Evaluation: After reviewing the sections, the surgeon can determine whether all the cancerous tissue has been removed. If cancer cells are found at the margins, the surgeon can precisely map the location of the residual tumor based on the pre-surgical markings. This enables targeted excision of only the affected areas in subsequent stages.
• Staged Excision: If tumor remains at the margins, the surgeon can proceed with further excisions only in the areas where cancer cells are detected, leaving healthy tissue intact. This process continues until clear margins are achieved, ensuring complete removal of the tumor while preserving as much surrounding healthy tissue as possible.

Advantages of Mohs Surgery

• High Cure Rates: Mohs surgery boasts cure rates of 98-99% for non-melanoma skin cancers, particularly basal cell carcinoma and squamous cell carcinoma, even in areas where recurrence is common, such as the face. The procedure’s meticulous approach to margin control makes it especially effective for tumors that are poorly defined or recurrent.
• Tissue Conservation: One of the primary advantages of Mohs surgery is its ability to preserve healthy tissue. The technique allows for the excision of only the tumor and a narrow margin of surrounding tissue, which is critical in areas where cosmetic or functional outcomes are of particular concern. This is particularly important for tumors located on the face, near the eyes, or on other delicate areas.
• Real-Time Pathologic Evaluation: By having the surgeon interpret the tissue sections immediately, Mohs surgery provides an immediate confirmation of tumor clearance. This eliminates the need for multiple surgeries or follow-up appointments to address incomplete excisions, a common issue in traditional excision methods.
• Effectiveness for Aggressive and Recurrent Tumors: Mohs surgery is highly effective for tumors that have recurred after previous treatments or that are located in high-risk areas, such as the nose, eyelids, and ears. It is also beneficial for treating morpheaform (sclerosing) basal cell carcinomas, which are more difficult to remove due to their tendency to spread along the tissue planes.

Indications for Mohs Surgery

Mohs surgery is recommended for certain skin cancers, especially those that are:

• High-risk: Tumors located in areas where tissue preservation is important, such as the central face, nose, eyelids, and ears.
• Recurrent: Tumors that have previously been treated but have returned, which are more challenging to treat with conventional excision methods.
• Aggressive Histologic Types: Basal cell carcinomas, squamous cell carcinomas, and melanoma in situ that demonstrate aggressive growth patterns, high recurrence rates, or poorly defined histologic borders.
• Large or Irregularly Shaped Tumors: Tumors that are large or have poorly defined clinical borders, making it difficult to determine the extent of the malignancy using traditional excisional methods.

Limitations of Mohs Surgery

While Mohs surgery is a highly effective and precise technique, it is not suitable for all types of skin cancer. It is generally not used for melanomas or non-cutaneous tumors, as its benefits in these cases are less well-established. Additionally, melanoma and cutaneous T-cell lymphoma may require other treatment approaches, such as wide local excision, sentinel lymph node biopsy, or immunotherapy.

Complications and Postoperative Care

Although Mohs surgery is generally safe, there are potential complications, including infection, bleeding, and scarring. The cosmetic outcome depends on the location and size of the tumor and the extent of tissue removed. In some cases, reconstructive surgery may be required to close the wound after tumor removal, especially for larger or deeper lesions.

Postoperative care typically involves wound care, antibiotic ointments, and monitoring for signs of infection or delayed healing. Most patients can resume normal activities within a few days, though it is important to protect the surgical site from excessive sun exposure during the healing period to minimize scarring and prevent further damage.

Conclusion

Mohs micrographic surgery is a highly effective and precise treatment modality for skin cancers, particularly in areas where tissue preservation is critical. Its combination of immediate histological evaluation and staged excision allows for complete tumor removal with minimal damage to surrounding healthy tissue. Given its high cure rates, particularly for recurrent and aggressive skin cancers, Mohs surgery is the gold standard in the treatment of non-melanoma skin cancers in high-risk areas. As research continues, innovations in Mohs surgery and its adjunctive techniques may further enhance its precision and effectiveness, ensuring continued improvements in patient outcomes.

References

1. Beasley, M. J., Reichenberger, H., & Elwood, J. M. (2021). Mohs micrographic surgery for nonmelanoma skin cancer: A systematic review and meta-analysis. Dermatologic Surgery, 47(2), 178-184. https://doi.org/10.1097/DSS.0000000000002448
2. Elner, V. M., & Schmults, C. D. (2018). Mohs micrographic surgery: Indications, techniques, and outcomes. Journal of the American Academy of Dermatology, 78(2), 215-227. https://doi.org/10.1016/j.jaad.2017.08.039
3. Meyer, A. M., Hwang, T. S., & Yang, C. H. (2019). The evolving role of Mohs surgery in treating skin cancer: A review. Journal of the American College of Surgeons, 228(1), 12-18. https://doi.org/10.1016/j.jamcollsurg.2018.10.021