Abstract

Malignant Melanoma (MM) account for 1% of all skin cancers and third most common skin cancer. MM are notorious for a wide spectrum of tumor morphology, and late and distant metastasis. MM metastasizing to the breast is relatively rare, and when presenting with a deceptively bland histology poses a diagnostic pitfall, especially where the history of primary melanoma is unknown.

 A 46-year-old-female presented with multiple self-palpated right breast masses. Mammography showed three-poorly-circumscribed-masses measuring 1.5, 1.1 and 0.9 cm, located a few-centimeters from nipple. Biopsy revealed mildly atypical discohesive cells with abundant eosinophilic cytoplasm, bland nuclei, indistinct nucleoli, and rare intranuclear-inclusions. Given the location and histology, the findings seemed most consistent with histiocytoid variant of invasive lobular carcinoma(HV-ILC). Typically HV-ILC shows loss of e-cadherin expression, lack myoepithelial cell markers, and could be triple negative. The tumor cells in our case showed negative/reduced expression of e-cadherin, and complete loss of estrogen receptor on immunohistochemistry consistent with HV-ILC.

On careful review of the patient chart, a very remote history of MM of left flank involving sentinel lymph node was noted, and they received wide-local-excision with adjuvant-immunotherapy without evidence of distance metastasis on imaging. This history and unusual morphology prompted evaluation for melanoma by immunohistochemistry. The tumor cells were diffusely-positive for SOX-10, Melan-A, and focal-positivity for HMB-45. A final diagnosis of metastatic melanoma to the breast was made. This case highlights the significance of obtaining a detailed clinical history and use of immunohistochemistry especially when evaluating relatively bland discohesive breast neoplasms with unusual cytomorphology.