A case report: axillary ALK-positive anaplastic large-cell lymphoma mimicking an infectious abscess in an adolescent

Abscess-like presentations are common in surgical practice, but malignant soft-tissue and lymphoid disorders can occasionally imitate infection and delay definitive treatment. Anaplastic large-cell lymphoma (ALCL) is a CD30-positive T-cell lymphoma that may involve skin, lymph nodes, or soft tissue and can show extensive necrosis, inflammatory change, and systemic symptoms.

A 17-year-old female student presented with a 3-week history of progressive painful erythema and swelling of the left axilla after ineffective intravenous antibiotic treatment elsewhere. On admission, the lesion was large, indurated, tender, and clinically suspicious for a soft-tissue infection with possible abscess formation. Incision and drainage yielded only scant purulent fluid but abundant friable nodular tissue, and cultures were negative. Persistent fever, local progression, lymphadenopathy, and poor response to antimicrobial therapy prompted multidisciplinary reassessment. Histopathology of the solid tissue demonstrated large pleomorphic lymphoid cells, and immunohistochemistry showed strong CD30 and ALK expression, establishing ALK-positive ALCL. The patient was transferred to hematology and received initial cytoreductive therapy with brentuximab vedotin and short-course zeprumetostat, after which the local tumor burden decreased and delayed wound closure was performed. She subsequently received five cycles of brentuximab vedotin plus CHP and chidamide maintenance after complete remission.

A presumed abscess that yields little pus but contains solid friable tissue should not be managed as infection alone. In refractory, culture-negative, or biologically discordant soft-tissue lesions, early biopsy of the cavity wall and solid components may help reduce diagnostic delay and redirect care toward malignancy-specific treatment.