Myxoid Variant of Primary Cutaneous Anaplastic Large Cell Lymphoma Mimicking Soft Tissue Sarcoma: Diagnostic Pitfalls...

Primary Cutaneous Anaplastic Large Cell Lymphoma (PCALCL) is a CD30-positive T-cell lymphoma that typically manifests as a dermal nodule or tumor with favorable prognosis. Rare morphologic variants with prominent myxoid stroma can closely mimic myxoid soft tissue sarcomas and lead to misdiagnosis. A 40-year-old man presented with a slowly enlarging ulcerated mass on the left thigh that was radiologically regarded as a superficial soft tissue sarcoma, prompting wide excision with sentinel lymph node biopsy. Histological examination showed a multinodular, dermal, and subcutaneous tumor composed of highly pleomorphic hallmark-type, rhabdoid, epithelioid, and spindle cells, along with multinucleated forms embedded in abundant myxoid stroma, and associated with delicate curvilinear vessels. Immunohistochemically, all tumor cells demonstrated strong and diffuse CD30, CD2, and CD4 expression; and weak positivity for EMA. They were negative for CD3, CD5, CD7, CD8, TIA-1, and perforin, and also showed no expression of ALK or of epithelial, melanocytic, myogenic, vascular, or B-cell markers. These findings support the diagnosis of ALK-negative myxoid PCALCL. Comprehensive staging with positron emission tomography-computed tomography and bone marrow biopsy revealed no extracutaneous disease, and the patient achieved a complete metabolic remission after 6 cycles of CHOP-E chemotherapy, remaining disease-free for 40 months after diagnosis. This case broadens the clinicopathologic spectrum of PCALCL and highlights that infiltrative and myxoid CD30-positive tumors of the extremities may masquerade as sarcoma, underscoring the importance of including CD30 and T-cell markers in the evaluation of pleomorphic myxoid soft tissue tumors.