If a metastatic melanoma is found in an axillary lymph node but no primary melanoma site is identified, what primary site is assigned?

When metastatic melanoma is found in an axillary lymph node without an identifiable primary site, the correct coding refers to the skin as the likely origin of the melanoma. Melanoma is a type of skin cancer, and while the primary site is unknown, it is most often associated with skin lesions. Therefore, assigning the primary site as "C44.9 Skin, NOS" acknowledges the probable origin of the disease.

Different coding options can reflect various aspects of the disease, such as the specific anatomical location (axillary lymph node) or a more general category (unknown primary). However, since melanoma predominantly arises from the skin, and the axillary lymph node is simply a site of metastasis, indicating "Skin, NOS" is appropriate in this scenario.

Choosing an unknown primary site could also be valid in certain contexts, but in the case of melanoma, where typical patterns suggest skin as the primary source, the assignment to the skin aligns with established conventions in oncology coding.