[HAVCR2-mutated subcutaneous panniculitis-like T-cell lymphoma presenting with bone marrow infiltration and rapidly fatal hemophagocytic lymphohistiocytosis].

A 37-year-old man presented with recurrent fever. Diagnosis was challenging due to the lack of localized physical findings; however, subcutaneous panniculitis-like T-cell lymphoma (SPTCL) was eventually confirmed through multiple bone marrow biopsies. The patient developed rapidly progressive liver failure and hemophagocytic lymphohistiocytosis (HLH), resulting in a severe bleeding tendency. Despite receiving massive blood transfusions and sequential treatments with corticosteroids, etoposide, and CHP chemotherapy even before the definitive diagnosis, the patient died of cerebral hemorrhage approximately one month after admission. Autopsy revealed tumor infiltration in systemic adipose tissue and bone marrow. Genetic testing identified a homozygous germline HAVCR2 mutation (p.Y82C). While SPTCL is a rare subtype of cytotoxic T-cell lymphoma generally associated with a favorable prognosis, cases harboring HAVCR2 mutations can be complicated by severe HLH and follow a fulminant course. Detailed clinical reports of such severe cases are scarce. Our findings suggest that early diagnosis and prompt initiation of chemotherapy are crucial for managing severe SPTCL.