Antibiotics after breast cancer may affect survival rates

Antimicrobial exposure may impact survival in triple-negative breast cancer.


Breast cancer is the most common cancer in women worldwide. The immune system plays a crucial role in determining outcomes. Triple-negative breast cancer (TNBC) is the most lethal subtype, disproportionately affecting ethnic minorities and those with lower socioeconomic status. Despite advances in therapy, TNBC has inferior outcomes compared to non-triple-negative breast cancer.

Lower absolute lymphocyte count (ALC) is prognostic for breast cancer mortality, and higher baseline tumor-infiltrating lymphocyte (TIL) density is associated with improved outcomes in TNBC. The gut microbiota may influence cancer outcomes by modulating host immunity, and there is growing interest in its impact on treatment response.

The use of antibiotics during cancer treatment is known to disrupt the gut ecosystem, and studies have reported conflicting results on the impact of antibiotics on breast tumor growth and response to immunotherapy. This study investigates whether antimicrobial exposure impacts clinical outcomes in patients with TNBC who are not treated with ICIs.

The hypothesis is that increasing antimicrobial exposure during curative intent TNBC treatment and follow-up impairs lymphocyte-mediated antitumor immunity, leading to adverse survival outcomes.

Stanford Medicine researchers found that women with triple-negative breast cancer who took multiple antibiotic prescriptions within three years after their cancer diagnosis had higher chances of disease recurrence and death than those who took fewer courses of antibiotics.

The study showed that the effect on survival was not due to differences in cancer severity; the risk increased with the total number and types of antibiotics prescribed.

Julia Ransohoff, MD, a hematology and medical oncology fellow at the Stanford School of Medicine, said, “Each additional antibiotic increased the risk of death between 5% and 18% relative to patients who weren’t prescribed antibiotics. It is important to interpret these findings with caution, however. We can’t let life-threatening infections go untreated. But this study suggests that we consider how best to treat them without raising the risk of cancer recurrence.”

A researcher from Stanford University said, “These findings offer insight into the role of the immune system and factors that may perturb its function in fighting the most aggressive type of breast cancer. Gaining a better understanding of this process will be important to guide patient care.”

A new study suggests that antibiotics may impact the immune system’s ability to fight cancer, specifically in triple-negative breast cancer cases. The study, which analyzed data from 772 women diagnosed with non-metastatic triple-negative breast cancer and treated between 2000 and 2014, found that treatment with antimicrobials, including antibiotics, was linked to a decrease in lymphocytes in patients’ blood.

Lymphocytes are immune cells that help fight cancer, and the study found a strong association between the use of antibiotics and decreased survival rates.

The study did not prove causation but only showed an association. The researchers suspect the link lies in the gut microbiome, as antibiotics can harm the beneficial bacteria that support the immune system. However, the researchers caution that the study does not mean that cancer patients treated with antibiotics should panic and that further research is needed to confirm the findings.

The study looked at the medical records of 772 female patients diagnosed with triple-negative breast cancer from 2000 to 2014, who were treated at Stanford University or Palo Alto Medical Foundation and observed for at least five years. The researchers analyzed the use of antimicrobials, such as antibiotics and antifungals, and their association with the patient’s survival rates.

They found that higher total and unique antimicrobial exposure was associated with worse breast cancer-specific and overall survival rates. Patients with higher BMI, lower minimum ALC or ANC, or who underwent unilateral or bilateral mastectomy were more likely to use antimicrobials. The study suggests that using antimicrobials may affect the outcomes of triple-negative breast cancer patients.

The study investigated whether the use of antimicrobials (which includes antibiotics) in breast cancer patients affects their survival and response to chemotherapy. The researchers looked at factors such as disease severity, type of antibiotic exposure, and time elapsed since diagnosis. They found that certain types of antibiotic exposure were associated with lower survival rates, particularly in the first three years after diagnosis. However, they did not find a link between antibiotic use and response to chemotherapy.

Overall, the study provides valuable insights into the potential risks of antibiotics usage in breast cancer patients and underscores the need for personalized treatment plans that take into account individual patient characteristics and medical history.

Journal Reference:

  1. Ransohoff, J. D., Ritter, V., Purington, et al. Antimicrobial exposure is associated with decreased survival in triple-negative breast cancer. Nature Communications. DOI: 10.1038/s41467-023-37636-0


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