Background: The introduction of new treatments for hairy cell leukemia has resulted in improved patient survival but also engendered increasing concern about the possibility of excess second cancers. The available evidence is conflicting, with most risk estimates based on sparse numbers. To our knowledge, no study has evaluated cause-specific mortality in patients with hairy cell leukemia.

Methods: We quantified second cancer incidence and cause-specific mortality among 3104 two-month survivors of hairy cell leukemia who were reported to 16 population-based registries in the Surveillance, Epidemiology and End Results (SEER) Program between 1973 and 2002. Standardized incidence ratios (SIRs) and standardized mortality ratios (SMRs) were used to quantify the risk of second cancers and causes of death, respectively. The cumulative probability of a second cancer among survivors of hairy cell leukemia was calculated using a competing risk model. All statistical tests were two-sided.

Results: Mean follow-up of hairy cell leukemia survivors was 6.5 years (range, 2 months-29.3 years). Second cancer risk was statistically significantly elevated (SIR = 1.24, 95% confidence interval [CI] = 1.11 to 1.37) compared with the general population. Survivors had statistically significantly higher risks of Hodgkin lymphoma (SIR = 6.61, 95% CI = 2.13 to 15.42), non-Hodgkin lymphoma (SIR = 5.03, 95% CI = 3.77 to 6.58), and thyroid cancer (SIR = 3.56, 95% CI = 1.30 to 7.74) and a lower risk of lung cancer (SIR = 0.63, 95% CI = 0.42 to 0.90). The cumulative probability of all second cancers was estimated to be 31.9% (95% CI = 26.2 to 37.6) 25 years after hairy cell leukemia diagnosis. Among 10,000 hairy cell leukemia patients, a total excess of about 34 cancers, including 21 non-Hodgkin lymphomas, 2 Hodgkin lymphomas, and 7 solid tumors (including 2 thyroid cancers), might be observed per year. Deaths due to solid tumors were not elevated compared with the general population (SMR = 0.9), and there were statistically significant deficits in mortality due to both cardiovascular (SMR = 0.67, 95% CI = 0.56 to 0.80) and cerebrovascular (SMR = 0.61, 95% CI = 0.38 to 0.93) disease.

Conclusions: Patients with hairy cell leukemia are at increased risk of Hodgkin lymphoma, non-Hodgkin lymphoma, and thyroid cancer. The decrease in lung cancer incidence and smoking-associated vascular mortality may reflect an inverse association of tobacco use with hairy cell leukemia. Future studies should address the roles of immunologic impairment inherent to hairy cell leukemia, treatment modalities, and other factors as codeterminants of morbidity and mortality in hairy cell leukemia survivors.