Concurrent and mutations in melanoma of unknown origin presenting as a breast mass.

Background: Metastases represent a small percentage of the malignancies affecting the breast, and only 5% of melanomas originate from non-cutaneous sites. Multiple genetic aberrations have been associated with the development of melanocytic lesions, including V600E mutation. Mutations in gene have also been related to the pathogenesis of multiple malignancies.

Purpose/method: This is the case of a 28-year-old female who presented with a tender, palpable mass in the upper outer quadrant of the right breast. Ultrasound showed a 1-cm solid mass, initially diagnosed as invasive ductal carcinoma on biopsy. During pre-operative workup, a second mass was identified and biopsied. Immunohistochemical stains performed on the second mass biopsy demonstrated that the neoplastic cells were positive for cytokeratin AE1/3, pan-melanoma, tyrosinase, and SOX-10 and negative for CK7, CAM5.2, and GATA-3. Subsequent workup showed widespread metastatic disease involving the liver, lungs, bones, and brain. The brain metastasis tested positive for p.V600E and p.R130Efs*4 mutations. Thorough skin and eye examination did not reveal a primary melanoma.

Conclusion: Only few reports have been published of melanoma presenting as a breast mass. This is an interesting case due to the clinical presentation, diagnostic challenges, and genetic mutations profile.