Risk and survival of chronic myeloid leukemia after breast cancer: A population-based study.

BACKGROUND: We aimed to investigate the risk and survival of chronic myeloid leukemia (CML) after breast cancer (BC) diagnosis.

METHODS: We used the Surveillance, Epidemiology, and End Results 'SEER' database. Females, diagnosed with BC between 1992 and 2014, were selected and followed for the development of CML after a 6-month latency period from BC diagnosis. We used the Multiple Primary Standardized Incidence Ratios session of the SEER*Stat software (version 8.3.4) to calculate the Observed/Expected (O/E) ratios with 95% confidence intervals (CI). To calculate the overall survival, we performed an unadjusted Kaplan-Meier analysis using the SPSS software.

RESULTS: We included 474,866 females with BC, of which 178 were later diagnosed with CML. We found the risk of CML to increase significantly after BC diagnosis (O/E = 1.26, 95% CI: 1.08-1.45) and the risk was specifically higher within the first 5 years of diagnosis (O/E = 1.45, 95% CI: 1.16-1.8). When the risk was stratified by cancer stage, localized BC was associated with a significant increase in CML risk within 5 years of diagnosis (O/E = 1.4, 95% CI: 1.06-1.82), while regional BC was associated with a significant increase in CML risk after more than 5 years of diagnosis (O/E = 1.59, 95% CI: 1.09-2.25). Moreover, radiotherapy, chemotherapy, and presence of hormonal receptors were associated with a significant increase in CML risk in BC patients. The median overall survival of CML after BC was 28 months.

CONCLUSION: Breast cancer patients have an increased risk of developing CML and further investigation is required to establish the causes of this finding.