SKINIPEDIA - Skin Cancer: Melanoma Explained in Depth
Melanoma (Skin Cancer) Part IX: Mohs Micrographic Surgery
In recent years, Mohs Micrographic Surgery, which many physicians consider the most effective technique for removing basal cell and squamous cell carcinomas (the two most common skin cancers), is being increasingly used as an alternative to standard excision for certain melanomas. In this technique, one thin layer of tissue is removed at a time, and as each layer is removed, its margins are studied under the microscope for the presence of cancer cells. If the margins are cancer-free, the surgery is ended.
If not, more tissue is removed, and this procedure is repeated until the margins of the final tissue examined are clear of cancer. Mohs surgery thus can eliminate the guesswork in the removal of skin cancers and pinpoint the cancer’s location when it is invisible to the naked eye.
Mohs surgery differs from other techniques since the microscopic examination of all excised tissues during the surgery eliminates the need to “estimate” how far out or deep the roots of the skin cancer go. This allows the Mohs surgeon to remove all of the cancer cells while sparing as much normal tissue as possible. In the past, Mohs was rarely chosen for melanoma surgery for fear that some microscopic melanoma cells might be missed and end up metastasizing.
In recent years, however, efforts to improve and refine the Mohs surgeon’s ability to identify melanoma cells have resulted in the development of special stains that highlight these cells. These special stains are known as immunocytochemistry or immunohistochemistry (IHC) stains and use substances that preferentially stick to pigment cells (melanocytes), where melanoma occurs, making them much easier to see with the microscope.
For example, staining excised frozen tissue sections with a melanoma antigen recognized by T cells (MART-1) effectively labels/locates the melanocytes, helping to home in on melanomas. The MART-1-stained sections are processed and evaluated for the presence of tumor in the margins; certain signs such as nests of atypical melanocytes show that the margins are positive for melanoma and that further surgery must be done. If none of these signs are present, the surgery is concluded. Thanks to such advances, more surgeons are now using the Mohs procedure with certain melanomas.
Lymph Node Involvement
Once a melanoma has progressed beyond Stage II, it has spread beyond the original site. It is most likely to have reached the lymph nodes that are closest to the tumor.
Palpable nodes. To find out whether melanoma cells have escaped the primary tumor, the physician starts by feeling the nearby lymph nodes. When there is an enlargement or lump in a lymph node, it is described as “palpable,” meaning that the physician can feel it on physical examination.
Today, a lymph node that is palpable is almost always surgically removed. It is then sent to the pathology laboratory to be tested microscopically for the presence of malignant cells. If any are found, the rest of the nodes in that basin will also be removed, and treatments that stimulate the immune system and/or chemotherapy will be recommended.
Non-palpable nodes. The lymph nodes are not always palpable even when melanoma cells have spread beyond the original tumor. In the past, there was much debate about when to excise and examine the local lymph nodes. Some believed in a wait and see policy; others believed in removing all the nodes (radical node dissection) in the region of the tumor on the chance there were hidden cancer cells; this was called elective lymph node dissection, or ELND.
Melanoma Skin Cancer Part X
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