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

We aimed to investigate the risk and survival of chronic myeloid leukemia (CML) after breast cancer (BC) diagnosis. 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. 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. Breast cancer patients have an increased risk of developing CML and further investigation is required to establish the causes of this finding.