A Case of ALK-Negative Anaplastic Large Cell Lymphoma Presenting as a Solitary Cutaneous Nodule

Anaplastic large cell lymphomas (ALCLs) are a group of CD30 positive T-cell non-Hodgkin lymphomas, accounting for only 3% of all non-Hodgkin lymphomas. As per the 2017 World Health Organization updated classification, there are four variants of ALCL: anaplastic lymphoma kinase (ALK) positive, ALK negative, primary cutaneous, and breast-implant associated. The different variants of ALCL share overlapping clinical presentations and pathologic features, creating a diagnostic challenge. A 71-year-old woman with a past history of T-cell lymphoma presented with a progressively growing nodule on her back for approximately 3 months. Physical exam demonstrated a 8.0 x 8.0 cm pink nodular indurated plaque located on her left upper back. A punch biopsy of the lesion revealed medium to large mononuclear cells with nuclear pleomorphism, hyperchromasia, and scattered mitotic figures. Immunohistochemistry demonstrated cells that were positive for CD30 and negative for ALK. Based on clinical and histopathologic findings, a diagnosis of ALCL was rendered. Differential diagnosis included primary cutaneous ALCL and cutaneous involvement by systemic ALK(-) ALCL. This case demonstrates the importance of clinicopathologic correlation in diagnosing ALCL and guiding therapy.