First-Line Treatment Choice and Risk of Other Malignancies in US Veterans Diagnosed with Chronic Lymphocytic Leukemia and Small Lymphocytic Lymphoma

Introduction: Patients with chronic lymphocytic leukemia and small lymphocytic lymphoma (CLL/SLL) have a higher risk of developing other malignancies compared to the general population (Greene et al, J NCI 1978). Chemoimmunotherapy has previously been the mainstay of treatment and was associated with increased rates of other cancers (OC) (Thompson et al, Blood 2023). Targeted therapies such as Bruton tyrosine kinase inhibitors (BTKi) and BCL2 inhibitors were approved in the frontline setting in 2016 and 2019, respectively, and are now the standard of care for initial therapy (Shanafelt et al, NEJM 2019; Fischer et al, NEJM 2019). This study aims to compare the incidence of OC in patients with CLL/SLL treated with frontline therapies or managed with active surveillance.

Methods: This is a retrospective case-control analysis of patients diagnosed with CLL/SLL during or after 2016 using the Department of US Veteran Affairs Central Cancer Registry (VACCR). Cases were patients with CLL/SLL diagnosed with incident OC, excluding nonmelanoma skin cancers. Frontline treatment with chemoimmunotherapy, monoclonal antibodies alone, or targeted therapies, such as BTKi or BCL2 inhibitor, was the exposure of interest compared to patients on active surveillance. Patients were followed until date of OC, death, or last follow up. Descriptive statistics were used to summarize continuous and categorical variables. Logistic regression was used to analyze the risk of developing OC while adjusting for potential confounders.

Results: We identified 5244 patients with CLL/SLL who met inclusion criteria. Median follow up was 3.19 years (interquartile range [IQR] 1.61-5.14). The median age at diagnosis of CLL/SLL was 71.7 years (IQR 66.1-77.3) and most patients were white (78%) and male (97%). 3,460 (66%) patients were managed with active surveillance and 1,784 (34%) patients required frontline treatment: 1,318 (25%) targeted therapy, 329 (6%) chemoimmunotherapy, and 137 (3%) monoclonal antibodies alone. In patients treated with targeted therapies, patients were treated with ibrutinib (776, 59%), acalabrutinib (246, 19%), zanubrutinib (129, 10%), venetoclax (164, 12%), or combination of ibrutinib and venetoclax on a clinical trial (3, <1%).

505 (10%) patients were diagnosed with OC and 4739(90%) patients did not develop OC during the follow up period after diagnosis of CLL/SLL. Types of OC observed included neoplasms of the lung (120, 24%), prostate (105, 21%), gastrointestinal tract (72, 14%), hematologic malignancies (68, 13%), melanoma (45, 9%), kidney and bladder (43, 9%), head and neck (16, 3%), and other/unknown (36, 7%). More patients with OC had a history of tobacco use compared to those diagnosed with CLL/SLL without OC (70% vs 54%, p<0.0001). Fewer patients with OC had a history of alcohol use (60% vs 67%, p<0.0001).

In a logistic regression analysis adjusted for age at diagnosis of CLL, race, and tobacco and alcohol use patients treated with chemoimmunotherapy had a higher risk of OC compared to those on observation (OR 2.4, 95% CI: 1.7-3.3, p<0.0001) whereas patients treated with targeted therapies or monoclonal antibodies alone did not have a higher risk of OC (OR 1.1, 95% CI 0.9-1.4 and OR 1.4, 95% CI 0.8-2.6, respectively) compared to the patients on active surveillance. A higher proportion of patients with OC were deceased compared to those without OC, 219/505 (43%) vs 1261/4739 (27%), respectively (p<0.0001) at cutoff date.

Similar analyses of occurrence of OC in patients followed at tertiary centers including MD Anderson in Houston, Texas and Mayo Clinic in Rochester, Minnesota are ongoing and will be presented at the meeting.

Conclusion: Initial treatment with targeted therapies or monoclonal antibodies alone was not associated with an increased risk of OC in US veterans diagnosed with CLL/SLL during and after 2016. However, initial treatment with chemoimmunotherapy was associated with a significant increase of OC compared to patients with CLL/SLL managed with active surveillance.