Supplementary Material for: A Rare Clinical Case of Secondary Central Nervous System Involvement without Transformation in Hairy Cell Leukemia: Case Report and Literature Review

Introduction
Hairy cell leukemia (HCL) is an indolent B-cell lymphoma characterized by a specific genetic mutation, BRAF V600E, which affects the specific morphology and oncogenesis. For HCL, few reports regarding secondary central nervous system involvement (SCNSI) are available. Herein, we present the case of an 80-year-old woman who had a relapse of HCL with SCNSI.
Case presentation
The diagnosis of HCL was made in June 2015 after identifying BRAF V600E proteins by immunohistochemical analysis, and the disease was then controlled for 6 years by employing chemoimmunotherapy. In February 2021, the patient was admitted with neurological symptoms such as dizziness. Magnetic resonance imaging of the brain showed abnormal enhancement in the cerebrum, and cerebrospinal fluid analysis revealed neoplastic cells without transformation into large cells. Thus, the patient was diagnosed as having SCNSI in HCL.
Conclusion
We report a case of a rare clinical presentation of SCNSI in HCL with literature review.