Mohs surgery is widely recognized for its effectiveness in treating certain skin cancers. This article explains why this precise procedure is not typically used for melanoma, a serious form of skin cancer, by exploring their differing characteristics.
Understanding Mohs Surgery
Mohs micrographic surgery is a precise technique for removing skin cancer, performed layer by layer with immediate microscopic examination. The surgeon removes a thin layer of visible tumor and surrounding tissue, then examines the tissue’s edges and undersurface under a microscope. If cancer cells remain, the surgeon removes another thin layer only from the precise area where cancer was detected, repeating this process until no cancer cells are found. This method allows for complete tumor removal while preserving the maximum amount of healthy tissue.
Mohs surgery is primarily used for basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), the two most common types of skin cancer. Its precision makes it especially useful for cancers in cosmetically sensitive areas, such as the face, ears, and nose, or for large, aggressive, or recurrent tumors. It boasts high cure rates for BCC and SCC, often up to 99% for new cases.
Understanding Melanoma
Melanoma is a serious type of skin cancer that originates from melanocytes, the cells responsible for producing skin pigment. It is more dangerous than other skin cancers due to its aggressive nature and potential for rapid, unpredictable spread. Melanoma can spread not only locally but also to distant parts of the body, including lymph nodes and internal organs, a process known as metastasis.
Characteristics that may indicate melanoma include asymmetry, irregular borders, varied color, and a diameter larger than a pencil eraser. Changes in size, shape, or color of an existing mole are also concerning signs. Early detection is important because melanoma is highly treatable if caught before it spreads.
Key Differences in Cancer Behavior
The fundamental biological differences between the cancers typically treated by Mohs surgery and melanoma explain why Mohs is generally not the preferred treatment for melanoma. Basal cell carcinoma and squamous cell carcinoma usually grow locally and spread in a predictable, contiguous manner. This localized growth pattern makes Mohs surgery’s precise, layer-by-layer removal highly effective in ensuring all cancerous tissue is excised.
Melanoma, however, behaves differently. It has a higher propensity for early and unpredictable spread, even from a small primary tumor. Melanoma cells can travel through the lymphatic system or bloodstream to distant sites, sometimes forming “skip lesions” where isolated tumor cells are found beyond the visible lesion, or metastasizing to regional lymph nodes or organs. This unpredictable spread means that a local, precise excision focused solely on visible margins might miss microscopic disease that has already traveled.
The aggressive nature of melanoma cells and their potential for systemic dissemination requires a broader treatment approach. While Mohs provides excellent local control, it is primarily a local treatment. Melanoma cells can also be more challenging to identify under a microscope in frozen sections, which are used during Mohs surgery. Due to its metastatic potential, melanoma treatment often requires removing a wider margin of surrounding healthy tissue to capture any potential skip lesions and may involve systemic therapies to address potential spread throughout the body, which Mohs alone cannot achieve.
Standard Melanoma Treatment Approaches
Given melanoma’s aggressive nature and potential for widespread dissemination, standard treatment protocols differ from those for localized skin cancers. The primary surgical treatment for melanoma is wide local excision (WLE). This procedure involves removing the melanoma along with a significant margin of surrounding healthy tissue to ensure all cancer cells, including potential skip lesions, are removed. The size of the margin depends on the melanoma’s thickness and other characteristics.
Sentinel lymph node biopsy (SLNB) is often performed to assess if melanoma has spread to nearby lymph nodes. During this procedure, the lymph nodes closest to the tumor are identified and removed for examination. If cancer cells are found in these sentinel nodes, it indicates a higher stage of melanoma and informs further treatment decisions.
For advanced or metastatic melanoma, treatment extends beyond local surgery to include systemic therapies. These can involve immunotherapy, which harnesses the body’s immune system to fight cancer, or targeted therapy, which focuses on specific genetic mutations within cancer cells. These systemic treatments address cancer cells that may have spread throughout the body, highlighting why a purely local surgical approach like Mohs is insufficient for most melanomas.