Breast cancer in chronic lymphocytic leukemia patients: Characteristics and survival outcomes.

e13868 Background: Chronic lymphocytic leukemia (CLL) is associated with genetic mutations (e.g. TP53) and immune dysregulation, predisposing patients to second primary malignancies. Breast cancer is the most common malignancy in women with outcomes significantly influenced by tumor biology and stage at diagnosis. The coexistence of CLL and breast cancer represents a unique clinical scenario, as CLL-related immune dysfunction and therapies may impact breast cancer risk, tumor characteristics, and survival. This study aims to evaluate the clinical features and survival outcomes of breast cancer patients with CLL. Methods: Using the SEER database, two cohorts were created: breast cancer patients with CLL (study group, n = 677) and breast cancer patients without CLL (1,044,351). A matched control cohort of 400,741 patients was selected based on age, race and year of diagnosis using the ‘MatchIt’ package in R. Statistical analyses, including chi-square tests, Kaplan-Meier survival analysis, and logistic regression, were used to assess differences in tumor characteristics and survival outcomes. Results: Patients with CLL were most frequently diagnosed with breast cancer between ages 70–74 (20.09%), compared to 65–69 years in the control group (19.12%). The majority of both groups were White (study: 90.84%, control: 82.60%). CLL patients with breast cancer had more advanced disease at diagnosis (T1 50.52% vs. 71.95%, metastasis 4.87% vs. 1.75%; p < 0.001). The study group exhibited higher rates of HER2 positivity (10.19% vs. 7.14%) and triple-negative breast cancer (TNBC) (6.65% vs. 4.77%), while the prevalence of ER-positive (81.68% vs. 82.28%) and PR-positive tumors (69.28% vs. 70.61%) was comparable between the groups. Higher odds of TNBC were observed in the study group; however, the results were not statistically significant (OR 1.16; p = 0.33). Kaplan-Meier analysis showed worse cause-specific survival in CLL patients with breast cancer (restricted mean survival: 207.99 months vs. 233.54 months in controls; p < 0.001). They had an increased hazard (HR- 2.07, p < 0.001) for overall survival and for cause-specific survival (HR- 2.11, p < 0.001) compared to the control group. Conclusions: Breast cancer patients with CLL have more advanced disease at presentation and significantly worse survival outcomes compared to their counterparts. The increased prevalence of triple-negative breast cancer (TNBC) and HER2-positive subtypes suggests more aggressive tumor biology, potentially driven by CLL-related immune dysfunction, treatment and genetic factors. These findings underscore the importance of heightened surveillance and tailored management strategies for breast cancer patients with CLL.