Assessment of second primary malignancies among treated and untreated patients with chronic lymphocytic leukemia using real-world data from the USA.

Aim: Improved management of chronic lymphocytic leukemia (CLL) has resulted in a growing population of CLL survivors; these patients have a higher risk of developing second primary malignancies (SPMs) versus the general population. This retrospective cohort study aims to assess the timing, frequency, incidence and types of SPMs in treated and untreated patients with CLL in the USA, using the Surveillance, Epidemiology, and End Results (SEER) Medicare database, which links a nationally representative cancer registry with Medicare claims data. Patients & methods: Patients aged ≥66 years with newly diagnosed CLL between 1 January 2010 and 31 December 2016, who were enrolled in Parts A and B of Medicare for ≥12 months pre-diagnosis of CLL were selected from the database. Patients were assessed for ≥36 months until the end of continuous enrollment in Medicare Parts A, B and D, a switch to a health maintenance organization, death, or end of the study period (December 2019). Results: Of 3053 patients included in the analyses, 620 (20.3%) were treated and 2433 (79.7%) were untreated within 36 months of diagnosis. Overall, 638 (20.9%) patients developed a SPM, 26.8% of patients in the treated cohort and 19.4% of patients in the untreated cohort. The most common SPMs for both cohorts were squamous cell carcinoma and acute myeloid leukemia. Among the 166 treated patients who developed a SPM, a greater proportion developed their first SPM after treatment initiation versus those who developed their first SPM prior to treatment initiation (p < 0.001). A significantly lower percentage of patients who received targeted therapy developed a SPM (p < 0.05) versus patients treated with anti-CD20 + chemotherapy. Conclusion: Findings indicate that treatment type and timing can affect SPM development in patients with CLL. Combined with previous findings, this can help inform best practices in monitoring for SPM in patients with CLL.