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Case Reports

Abstract

A 67-year-old woman presented with gradual skin thickening progressing to diffuse pink nodules on the left arm and breast with lymphedema. A history of Stage IV ER+/PR+/HER2- inflammatory left breast invasive ductal carcinoma with nodal, skin, and bone metastases was noted, along with pleomorphic mantle cell lymphoma (PMCL) of the left nasal sinus, secondary HLH, and Guillain-Barré syndrome. Breast cancer had been previously treated with combination hormonal/chemotherapy and radiation treatment. PMCL was treated with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone with etoposide. A trephine biopsy of a left breast nodule was performed, with the intention of repeating phenotyping to direct potential therapy for metastatic carcinoma. Routine histopathology demonstrated a poorly differentiated neoplasm in the superficial dermis with mitotic figures, infiltrative growth, and high-grade cytologic features. Epithelioid cytomorphology was suggested. The context of metastatic left breast carcinoma and high clinical suspicion initially favored cutaneous metastasis of known breast carcinoma. However, immunostaining was triple-negative for ER, PR, and HER2 in contrast to the primary malignancy, and keratin markers were negative; additional stains for AE1/AE3, p63, and CK7 were negative. CD20 and CD5 showed partial membranous expression, CyclinD1 and MUM1 showed strong expression, and next-generation sequencing analysis (NGS) revealed MYD88, CCND1, and MLL3 mutations. A diagnosis of cutaneous metastatic PMCL was rendered, masquerading as cutaneous metastatic breast cancer. She opted for palliative care and unfortunately succumbed to breast cancer. This rare case of PMCL in the skin highlights the role for NGS diagnosing poorly differentiated cutaneous neoplasia in patients with multiple primary tumors.