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7577 Background: HCL is a rare indolent leukemia that is more common in men, with a 4:1 male predominance. To date, no studies have characterized the potential difference in outcomes of HCL between male and female patients. Hence, we sought to evaluate the outcomes of female HCL patients using the HCL-PDR. Methods: The HCL Foundation sponsored the development of HCL-PDR to characterize the clinical features and outcomes of this rare leukemia. HCL-PDR is an international multicenter PDR that includes patient, disease and treatment information abstracted from medical records. Adult patients enrolled in the HCL-PDR were included in the study. Female patients with HCL were the study population, with males as the comparator. The primary endpoint was the time to next treatment (TTNT) in females compared to males. Secondary endpoints included response rates (RR) and predictors of TTNT. Responses were categorized as: complete response (CR) including CR/CRu (CR unconfirmed)/HR (hematologic response), and partial response (PR), which included PR/PRu (PR unconfirmed)/pHR (partial HR). CRu was defined as no disease in bone marrow (BM) without available blood counts and HR as blood counts meeting criteria for HR, but no available BM. Cox proportional hazard models were used to estimate the hazard ratios for TTNT risk. Results: 357 patients were included: 265 males and 92 females. Table shows baseline characteristics stratified by sex. Among the patients who had disease status assessed after first treatment (n=224, males 169 and females 55), there was no significant difference in RR. However, females had significantly longer median TTNT (17.6 years) relative to males (8 years, HR 0.54, 95% CI 0.32-0.91, p=0.02) that remained significant after adjusting for other variables (RR and BRAF mutation) in multivariable analysis (HR 0.32, 95% CI 0.11-0.97, p=0.04). Factors predictive of longer TTNT include female sex and CR (HR.0.26, 95% CI 0.11-0.57, p=0.001). Conclusions: This is the first study to date reporting the clinical characteristics and outcomes in female HCL patients. The significantly longer TTNT in females compared to males may be related to factors such as underlying molecular features or hormonal influences. This finding needs to be explored further. [Table: see text]