By Admin at 26 Aug 2016, 15:46 PM

Postmenopausal women with breast cancer are often treated with aromatase inhibitor drugs, which block any remaining production of estrogen in the body.

Since many breast tumors are fueled by the presence of estrogen, the estrogen-reduction therapy is often effective at decreasing the size of breast tumors and lowering the risk of recurrence.

However, in some cases the cancer continues to grow and becomes resistant to the hormone-reduction therapy. Understanding why some tumors respond to the treatment and others do not has been an area of intense interest to researchers, and a new study has shed light on the mystery.

In an analysis of 22 breast tumors, 18 of them showed significant changes before and after treatment with aromatase inhibitors. While many of any given tumor’s initial gene mutations may have disappeared at the end of the four-month study period, new genetic mutations had often appeared.

Aromatase inhibitors are often used to shrink breast tumors prior to surgery, but the new research suggests it may be wise to reevaluate the tumor again just prior to surgery to monitor its changes and decide if a new course of treatment would be appropriate.

Matthew J. Ellis, study co-author and professor and director of the Lester and Sue Smith Breast Center at Baylor College of Medicine, told The Asco Post:

“In the post-treatment tumor samples, we found many new mutations or enrichment of mutations already seen in the pretreatment samples …

This means that under the environmental stress of the treatment, the tumors are spawning new sub-clones that subsequently can survive and grow despite therapy, and that is why we are having difficulty in the end treating estrogen receptor–positive breast cancer. We found this result in the majority of tumors we studied.”

In fact, only two tumors they analyzed showed a “stable genetic landscape,” meaning they remained largely unchanged after treatment with aromatase inhibitors. There were also two cases of “collision tumors,” which occur when two genetically different tumors become intertwined.

Study author Christopher A. Miller, an instructor in medicine at Washington University, explained to The Asco Post:

“This hints that collision tumors may be more common than we have previously realized. In these cases, estrogen suppression was the right approach for one of the tumors, but not the other, which limited the effectiveness of the treatment.”

For breast cancer patients, the study suggests that analyzing a tumor’s genome once at diagnosis may not be enough for effective treatment. Instead, scanning a tumor at multiple points during the treatment process may help establish more effective, personalized treatments.

Sources:
Nature Communications August 9, 2016
The Asco Post August 12, 2016

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