P644: THE LIFE EXPECTANCY OF PATIENTS WITH HAIRY CELL LEUKEMIA VERGES UPON THE LIFE EXPECTANCY OF THE GENERAL POPULATION: A POPULATION-BASED STUDY IN THE NETHERLANDS

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Background: At present, no other therapeutic strategy has substantially outperformed purine nucleoside analogues (PNAs)—introduced around the late 1980s and early 1990s—to manage hairy cell leukemia (HCL). The most recent population-based study in HCL showed that 10-year relative survival of HCL patients diagnosed in the Netherlands during 2001-2015 was 97%, 95%, and 83% in the age groups <60, 60-69, and ≥70 years, respectively (Dinmohamed AG et al. Blood; 2018). Given the improved longevity of HCL patients, relative survival rates fall short to inform on longevity across the entire patients’ life span. Aims: Studies estimating the life expectancy of HCL patients are hitherto lacking. Therefore, we assessed trends in the life expectancy of HCL patients from a historical and contemporary perspective. Methods: We selected all HCL patients diagnosed between 1989 and 2019—with follow-up for survival up to January 1, 2021—from the Netherlands Cancer Registry (N=1,828; median age, 60 years; interquartile range, 50-70 years; 78% males). We estimated the loss in expectation of life (LEL)—i.e., the difference between the life expectancy of patients and an age-, sex-, and period-matched group from the general population—using flexible parametric relative survival models. The LEL is interpreted as the average number of life years lost due to an HCL diagnosis. The LEL can vary markedly across ages because life expectancy is age-dependent. Therefore, the proportional LEL (PLEL) was estimated. These survival measures were presented by year of diagnosis for four ages at diagnosis (i.e., 40, 50, 60, and 70 years), stratified by sex. Results: The life expectancy of HCL patients increased gradually across all ages between 1989-2019, irrespective of sex (Fig A). It is noteworthy that HCL patients diagnosed in 1990 lost comparatively few life-years due to their diagnosis, ranging from a LEL of 1.7 to 3.9 life-years lost depending on age and sex (Fig B). Estimates for patients diagnosed in 2019 ranged from 0.8 to 1.9 life-years lost (Fig B). Over time, the decrease in LEL was most pronounced for younger patients (Fig B). For example, a 50-year-old male diagnosed with HCL in 1990, on average, has a LEL of 3.8 years (95% confidence interval [CI]: 2.1-5.5), whereas a male with a HCL diagnosis in 2019, on average, has a LEL of 1.0 years (95% CI, 0.3-1.7). The corresponding estimates for a 70-year-old male HCL patient were 2.3 (95% CI, 1.4-3.1) and 1.1 (95% CI, 0.6-1.7), respectively. The PLEL estimates also portrays that outcomes in HCL patients improved over time across all ages (Fig C). Nevertheless, there was a persistent age differential in the PLEL over time. More specifically, younger patients consistently have more remaining life-years than older patients, reflected in lower PLEL estimates in younger patients. Of note, the life expectancy estimates of female patients should be interpreted with caution by considering the wideness of the 95% CIs due to the comparative rarity of HCL in females to estimate the life expectancy accurately. Image:Summary/Conclusion: The life expectancy of HCL patients verges upon the life expectancy of the general population. This encouraging finding was already objectified around the early-1990s when PNA therapy was introduced for HCL management. Thereafter, the life expectancy gradually increased over time. Novel therapeutic strategies may reduce the minimal excess mortality encountered in contemporary diagnosed patients, particularly among the elderly.