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What is Melanoma In Situ

Dr. Sancy Leachman
Director - Melanoma & Cutaneous Oncology Program
Huntsman Cancer Institute

The term in-situ is a Latin term that means "in position." In the context of melanoma, this means that the malignant melanoma cells remain "in position" in the epidermis, the most superficial layer of the skin.

If the melanoma cells are able to escape from the epidermis and enter the next layer of skin (the dermis), then the melanoma is considered invasive. The reason that this distinction is important in melanoma is that if melanoma is caught at the in-situ stage, (also termed Stage 0), the prognosis is much better than if it is caught after it has become invasive.


If treated appropriately with complete excision including at least 0.5 cm margins of normal skin, melanoma in situ rarely recurs and has survival rates near 99%. Because in situ melanoma has not developed the capacity to spread yet, sentinel node biopsies are not required.


However, it is important that the excisions from in situ melanoma be reviewed carefully by a pathologist to assure that there are no cells that have begun to invade the dermis. If dermal invasion has occurred, even if it is only in a small area of the melanoma, the whole melanoma is considered invasive and wider surgical margins will be needed. As well, a sentinel lymph node biopsy might be considered, depending on how deep the invasion at that site was (as well as other features of the melanoma, such as how fast the cells were dividing).


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