Primary Central Nervous System ALK-Negative Anaplastic T-Cell Lymphoma is a Challenging and Uncommon Diagnosis Free

Primary central nervous system lymphoma (PCNSL) accounts for only 1% of all lymphomas and 6% of all tumors in the central nervous system. Most of these lymphomas are B-cell types, while T-cell types are less common. Anaplastic T-cell lymphoma with ALK-negative is the least common form of anaplastic T-cell lymphoma. It has a similar morphology but is more aggressive than ALK-positive variant. Smaller numbers of ALK-negative PCNSL have been reported. Herein, we report a case of cerebellar ALK-negative anaplastic T-cell lymphoma (ATCL) not only because of the unique location but also to highlight this entity to be considered in future diagnosis to avoid delay or misdiagnosis.

A 58-year-old woman with no significant past medical history presented with headaches, aphasia, confusion, short memory loss, and loss of control over her body. She had had similar episodes more than three months before. MRI demonstrated extensive enhancement of the leptomeningeal, pial, and pachymeningeal surfaces. Moreover, there are nodular mass-like areas along the cerebellar folia. Left suboccipital craniotomy with biopsy of left cerebellar lesion was performed. Histopathological examination revealed numerous large, atypical lymphocytes characterized by large-size, ovoid to irregular to lobated nuclei, vesicular chromatin, and vacuolated cytoplasm. These cells react positive to CD3, CD30, CD43, CD2, CD7CD56, and negative to ALK1, CD8, CD20, PAX5, CD5, CD10, CD15, CD34, CD138, EMA, p63, TdT, GFAP, CAM5.3, synaptophysin, SOX10, and EBER in situ

hybridization. No ALK separation is observed by FISH; however, three copies of the ALK gene are found on chromosome 2p23. ALK-negative ATCL was diagnosed based on all these findings.

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Primary central nervous system lymphoma (PCNSL) is extremely rare, and most lymphomas are B-cell types. Anaplastic T-cell lymphomas, ALK-negative lymphoma is a rare and most aggressive variant of T-cell lymphoma. Reporting this tumor is crucial to avoid delay or misdiagnosis.