Melanoma in situ of anal skin

This code signifies the presence of melanoma that is confined to the epidermis (in situ) and has not invaded the dermis, specifically located on the skin of the anus. It represents the earliest stage of melanoma, where malignant cells are present but have not spread beyond the outermost layer of the skin.

Apply this code when documentation clearly indicates a diagnosis of melanoma in situ affecting the anal skin, typically confirmed by biopsy. This diagnosis is often made following the excision of a suspicious lesion in the perianal region.

• Ensure the pathology report explicitly states "in situ" and specifies the "anal skin" as the primary site.
• Do not use this code for invasive melanoma of the anus; refer to codes in the C43 series for invasive lesions.
• Distinguish from melanoma of the anal canal (mucosa), which would be coded differently.