Flow Cytometry-Aided Early Diagnosis and Alectinib Response in Advanced ALK-Positive Large B-Cell Lymphoma: A Case Report

Anaplastic lymphoma kinase (ALK)-positive large B-cell lymphoma (LBCL) is an exceptionally rare subtype of B-cell lymphoma that typically arises independent of immunosuppression. Patients with stage IV disease have a particularly poor prognosis, with a median overall survival of approximately 1 year (95% confidence interval [CI], 0.8–1.5) and a 5-year survival rate of 5% (95% CI, 0–18%). Early diagnosis is often difficult because its morphological features may mimic those of solid tumors. In addition, no standard therapeutic regimen has been established, and many patients present with advanced disease and poor performance status that limit treatment options.We describe an elderly patient with ALK + LBCL who developed the disease while receiving immunosuppressive therapy for rheumatoid arthritis and systemic lupus erythematosus. Flow cytometry-aided early diagnosis by characterizing the distinct immunophenotype of the tumor. To our knowledge, this is the first reported case of an elderly patient (> 60 years) with ALK + LBCL treated with alectinib. Despite relapsed/refractory disease, the patient achieved tumor control for 10 months, suggesting that alectinib may represent a promising therapeutic option for this rare lymphoma.