Antibiotics Link to Triple-Negative Breast Cancer Mortality?

SAN ANTONIO – A small study suggests the frequent use of antibiotics among women with triple-negative breast cancer, may have an impact on overall and breast cancer–specific mortality.

The study was recently presented at the San Antonio Breast Cancer Symposium by Julia D. Ransohoff, MD, of Stanford (Calif.) University.

Gut-associated lymphoid tissues are the largest component of the immune system. They influence both local and systemic immune responses, but the use of antimicrobials can decrease circulating and tumor-infiltrating lymphocytes that effect the immune repertoire and in turn, the survival of women with triple-negative breast cancer.

Ransohoff and colleagues hypothesized that increasing antimicrobial exposure in the presence of time-varying absolute lymphocyte counts may lead to higher overall and breast cancer–specific mortality. Their analysis is based on data from the population-based Surveillance, Epidemiology, and End Results registry and electronic medical records from Stanford University and Sutter Health. It included 772 women who were treated for triple-negative breast cancer between 2000 and 2014. The women were followed for an average of 104 months.

In an earlier analysis of this same group, Ransohoff found that higher minimum absolute lymphocyte counts were associated with lower overall mortality (hazard ratio, 0.23; 95% confidence interval, 0.16-0.35) and breast cancer mortality (HR, 0.19; 95% CI, 0.11-0.34) The association between higher peripheral lymphocyte counts and tumor-infiltrating lymphocytes was significant.

In the analysis of relationships between antibiotic use and mortality, 85% of women (n = 654) were prescribed antibiotics after having been diagnosed with triple-negative breast cancer. The death rate among patients who were prescribed antibiotics was 23% (153/654), compared with 20% (24/118) among the patients who were not treated with antibiotics (which accounts for 15% of the entire group).

For total antibiotic exposure, the HR for overall mortality was 1.06 (95% CI, 1.03-1.09; P < .001) and 1.07 for breast cancer–specific mortality (95% CI, 1.04-1.10; P < .001). For unique antibiotic exposure (not counting repeat prescriptions of the same antibiotic), the HR for overall mortality was 1.17 (95% CI, 1.12-1.22; P < .001) and 1.18 for breast cancer–specific mortality (95% CI, 1.12-1.24; P < .001).

“These were all statistically significant associations derived from a statistical model that takes into account baseline patient characteristics, so the reported hazard ratios, to the best of our ability, represent the risk of death associated with antibiotic use adjusted for other baseline covariates. We’ve attempted to account for differences at baseline that may indicate patients are sicker, and so the reported risk represents mortality related with antibiotic exposure,” Ransohoff said.

Elucidating the role of the microbiome in mediating absolute lymphocyte counts and immune response may inform interventions to reduce triple-negative mortality, she said.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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