Estrogen-Lowering Therapy May Cause Mutations in Breast Cancer Tumors

Nurse Assisting Patient Undergoing Mammogram in hospital
Nurse Assisting Patient Undergoing Mammogram in hospital

Therapies for lowering estrogen are a common treatment for certain types of breast cancers, but tumors may end up mutating and becoming resistant in response, according to some new findings.

The research in question comes courtesy of the McDonnel Genome Institute at Washington University and suggests that periodic scanning of a tumor’s genome—as opposed to once when first diagnosed—may be useful for better anticipating the course of the disease.

Breast cancer tumors that fall into the “estrogen-receptor-positive” category will grow in response to the body’s estrogen levels. Part of the treatment for this type of cancer is to use drugs to suppress estrogen production and make the tumor shrink enough that it can be surgically removed.

The researchers looked at the genetics of 22 breast tumors from postmenopausal women both before and after a four-month treatment with estrogen-suppressors. They found that in most of the post-treatment samples, new mutations or enrichments of pre-existing mutations had appeared.

This poses a potential threat since the mutations induced by the treatment could end up making the tumors more able to persist and spread even after the majority has been removed. Based on this finding, the researchers recommend that anyone who has undergone treatment with the drug in question (aromatase inhibitors) should have their tumor’s genome re-checked immediately prior to surgery so that any mutations which could potentially affect the risk of breast cancer relapse are identified.

Strictly speaking, the study wasn’t able to establish that the aromatase inhibitor therapy was the cause for the mutations. Doing that would require a larger sample size and a control group, and there are very obvious ethical issues that come up when you propose not treating someone’s cancer.

Tumors, from breast cancer or otherwise, are not known for genetic stability and 18 of the 22 samples showed highly complex and dynamic genomes. Still, whether or not the estrogen-lowering therapy could be strongly linked to tumor mutations or not, the idea of double-checking the genome prior to surgery is a sound proposal that will hopefully get explored further.

Strait, J., “New study shows breast tumors evolve in response to hormone therapy,” Washington University School of Medicine web site, August 9, 2016;, last accessed August 9, 2016.