Adjuvant breast cancer treatment associated with additional cancer risk

1. In a cohort of more than 20 000 breast cancer patients followed for a median of 5 years, the use of adjuvant chemotherapy and radiation was associated with increased risk of bone marrow neoplasms.

Evidence Rating Level: 3 (Average)

Study Rundown: Despite the significant survival improvement associated with adjuvant breast cancer therapies, previous patient database studies have demonstrated an increased incidence of bone marrow neoplasms (MN) associated with adjuvant chemotherapy and radiation use in breast cancer patients. However, the exact incidence of this effect is not well known. The purpose of this large retrospective cohort study was to further evaluate the risk of treatment associated MN from a large United States breast cancer patient database. The study analyzed the patient outcomes of over 20 000 early breast cancer patients for development of new MN. After a median follow-up of 5.1 years, the authors demonstrated that 50 patients (0.25%) developed treatment induced MN. This incidence was significantly greater than the expected incidence based on previous national cancer surveillance data. Furthermore, although the overall incidence was low, the cumulative incidence of MN doubled between 5 years to 10 years of follow-up. The results of this retrospective study support a small, but potentially significant long-term risk factor of MN in patients that undergo adjuvant breast cancer therapies. The main limitation of this study is the retrospective study design, which did not collect the dosage information of the chemotherapy and radiation treatment delivered. Additional prospective, longitudinal patient databases are needed to accurately quantify this observed association.

Click to read the study in JCO

Relevant Reading: Risk of leukemia after chemotherapy and radiation treatment for breast cancer

In-Depth [retrospective cohort]: In this study, outcome data from breast cancer patients was collected from the Breast Cancer Outcomes Database, a multi-center database comprised of eighteen academic institutions in the United States. Female patients who presented with Stage I to III breast cancer from 1997 to 2007 were included with a primary outcome of development of MN. In total, 20 603 breast cancer patients were included in the analysis. The observed incidence of MN was compared to the Surveillance, Epidemiology, and End Result (SEER) database incidence data. Fifty patients (myeloid, n=42; lymphoid, n=8) developed MN with a median follow-up of 5.1 years. The observed incidence is significantly higher than the expected incidence derived from the SEER database (observed-to-expected ratio: 3.6; 95% CI: 2.6-4.6; p<0.001). Patients who developed MN were similar in race, chemotherapy exposure, and breast cancer staging, but were significantly older (median age: 59.1 vs. 53.9; p=0.03) compared to patients who did not develop MN. The cumulative incidence of MN doubled between 5 and 10 years (0.24% and 0.48%, respectively) of follow-up.

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