Efficacy of ruxolitinib for HAVCR2 mutation‐associated hemophagocytic lymphohistiocytosis and panniculitis manifestations in children

Summary Frequent germline mutations of HAVCR2 , recently identified in subcutaneous panniculitis‐like T‐cell lymphoma (SPTCL), are associated with an increased risk of hemophagocytic lymphohistiocytosis (HLH). However, SPTCL‐HLH represents a challenge because of the difficulties in treatment with poor survival. Its malignant nature, specifically harbouring HAVCR2 mutations, has also been questioned. To better understand its pathology and treatment, we analysed the clinical data of six patients diagnosed at our centre. The median age at onset was 10.5 years (range, 0.8–12.4). Five patients presented with skin lesions of subcutaneous nodules/plaques and/or ulceration. All patients developed HLH; notably, one infant only had HLH without skin involvement. Histopathologically, only two patients were diagnosed with SPTCL and three were reported as panniculitis with no sufficient evidence of lymphoma. Genetically, germline homozygous mutation of HAVCR2 (p.Y82C) was identified in all patients, with a median diagnosis time of 4.6 months. All patients initially received corticosteroids, immunosuppressants or chemotherapy, achieving unfavourable responses. Strikingly, they responded well to ruxolitinib targeting inflammatory cytokines, allowing rapid disease resolution and/or long‐term maintenance of remission. The excellent efficacy of ruxolitinib highlights this disease as an inflammatory condition instead of neoplastic nature and indicates novel agents targeting key inflammatory pathways as an encouraging approach for this disease entity.