ALK-Negative Anaplastic Large Cell Lymphoma Presenting as an Extranodal Soft-Tissue Mass With an Unusual Alveolar Growth Pattern: A Diagnostic Challenge

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Anaplastic large cell lymphoma (ALCL) is a T-cell lymphoma which has been recognized to have a variable clinical presentation and a broad spectrum of histomorphologic features. Its variable histomorphologic appearances are sometimes diagnostically challenging for the pathologists since they can mimic sarcomas, melanomas and undifferentiated carcinomas. To our knowledge, a previous case of axillary soft-tissue mass of ALK-positive ALCL with an alveolar growth pattern has been so far reported in the literature. This alveolar appearance is unusual for ALCL. It can impose a diagnostic pitfall, particularly in extranodal soft-tissue masses. We report a case of ALK-negative ALCL that presented as an extranodal soft-tissue neck mass in an adult man. Histologically, it showed a characteristic alveolar growth pattern composed of well-defined nests of dyscohesive highly pleomorphic large neoplastic cells separated by thin fibrovascular septae. Morphologically, it mimicked sarcomas, carcinomas, melanoma and germ cell neoplasms. Initially, a histologic diagnosis of ALCL was not considered. However, the negative immunomarkers for the above mimickers and the strong CD30 positivity have raised the suspicion of anaplastic lymphomas. Further immunohistochemistry studies showed the neoplastic cells to be positive for CD4 and CD43. This case report emphasizes the potential diagnostic pitfalls associated with an ALK-negative ALCL when manifests as a soft-tissue mass with an alveolar growth pattern. Pathologists should be aware of this uncommon growth pattern in ALCLs. They should implement a broad panel of immunomarkers in soft-tissue masses of anaplastic pleomorphic cells with an alveolar morphology.

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