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Melanoma of Unknown Primary Presenting as a Single Back Mass

Siu-Yuan Lai Huang, Anitha Srinivasan, James Mariadason, Marc Wallack


In this report, we present a case involving the discovery of metastatic melanoma within a mid-right back mass with the clinical presentation of an epidermoid cyst, but the histological qualities of a lymph node. A 43-year-old male presented with a 5 cm x 5 cm cyst-like mass on his mid-right back that had become painful over the last year and consequently underwent three surgical procedures. First, initial excision of the back mass and histological examination resulted in a diagnosis of metastatic melanoma without epidermal involvement. This was followed by re-excision of the back mass site and sentinel node excision, and finally, lymph node dissection of the right axilla. Of the lymph nodes examined, the sentinel node in the right axilla alone showed evidence of melanoma. The absence of a primary lesion or any histological evidence of regression in a presumed primary site resulted in a diagnosis of melanoma of unknown primary, or occult primary melanoma. To our knowledge, this is the first documented case of an occult primary melanoma presenting as a single mass representing a lymph node in the back.


Malignant melanoma with unknown Primary; Malignant Melanoma within lymphatic tissue; Malignant Melanoma in the dermis and subcutaneous tissue; Malignant Melanoma in posterior trunk with no established Lymphatic drainage system

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