An Unusual Presentation of ALK-Negative Anaplastic Large Cell Lymphoma: A Case Report

Anaplastic large cell lymphoma (ALCL) is a rare but aggressive type of non Hodgkins lymphoma that develop from mature T cells. Case: A 73-year-old male presented with a swelling over the medial aspect of the right leg. An excision biopsy was performed, and histopathological examination revealed a malignant round cell neoplasm. Immunohistochemistry was negative for CD45, CD20, and CD3 showing strong, diffuse CD30 positivity. Based on diffuse CD30 positivity, further immunohistochemical markers, including ALK and additional T-cell markers were done and a diagnosis of ALK-negative ALCL was made.ALCL can rarely present with the absence of characteristic hallmark cells and negativity for CD45 and some of the T cell markers. CD45 and CD3 negativity can lead to misdiagnosis by omission of further markers. In this case, further lymphoid markers were done due to the diffuse CD30 positivity. Hence, ALK-negative ALCL is a diagnostic challenge. ALCL may rarely lack characteristic hallmark cells and show negativity for CD45 and certain T-cell markers, which can lead to diagnostic pitfalls if additional immunohistochemical workup is not performed. In the present case, diffuse CD30 positivity prompted further lymphoid marker evaluation, leading to the correct diagnosis. This highlights that ALK-negative ALCL remains a diagnostic challenge and highlights the importance of a broad immunohistochemical panel in atypical presentations.