Prognostic impact of morphological lymphocyte counts on aggressive adult T-cell leukemia/lymphoma: Japan ATL nationwide registry analysis.

Adult T-cell leukemia/lymphoma (ATL) is a lymphoid malignancy with poor prognosis. Although an increased tumor burden and impaired host immunity are recognized as adverse prognostic factors for aggressive ATL, the prognostic significance of morphologically normal and abnormal peripheral blood lymphocyte counts at the time of diagnosis has not been clarified. We analyzed 638 patients newly diagnosed with aggressive ATL enrolled since 2021 in a nationwide prospective registry across 152 Japanese institutions. Cutoff values derived from receiver operating characteristic curves for survival outcomes identified 860/μL for normal lymphocytes and 15,000/μL for abnormal lymphocytes. Patients with low normal lymphocyte counts had significantly poorer overall survival (OS; P < 0.001) and progression-free survival (PFS; P < 0.001) than those with higher counts. Elevated abnormal lymphocyte counts were significantly associated with shorter PFS (P = 0.004), but not OS (P = 0.496). In multivariate analyses incorporating eight established prognostic factors, a low normal lymphocyte count remained an independent predictor of shorter OS and PFS, whereas a high abnormal lymphocyte count independently predicted shorter PFS. These findings demonstrate that normal and abnormal lymphocyte counts are routinely measured, inexpensive, and rapidly available parameters, highlighting their value as practical and informative prognostic indicators of aggressive ATL.