Genomic tools and the era of tailored treatment in breast cancer
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In an era of precision medicine, we are reminded over and over that each person’s cancer is different. For women with early stage breast cancer, we have been able to use genomic information to analyze a tumor’s biology.

This information allows oncologists to personalize cancer care so that not all patients are treated the same. The most valuable example in breast cancer has been the OncotypeDX 21-gene recurrence score– a test examining 21 different genes.

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This test has been shown to predict the likelihood of recurrence for women with certain types of breast cancer, and more critically has been shown to identify which women with breast cancer benefit from chemotherapy, and which do not. It has been widely used for over a decade, creating a wealth of clinical familiarity and research experience.

To date, more than 600,000 women around the world have had this test done on their breast cancers. Recent studies conducted in the U.S. and Europe confirm that women with a low recurrence score have an excellent prognosis without needing chemotherapy; other studies have shown that real-world implementation of the 21-gene recurrence score lowers the use of chemotherapy without adversely affecting a woman’s prognosis.

The MINDACT trial, whose result were reported this week in the New England Journal of Medicine, analyzed whether a different genomic test – the 70-gene MammaPrint test — could also determine which women needed chemotherapy with early stage breast cancer.

The MINDACT trial confirmed that patients with certain breast cancers, who have a low clinical risk by stage and a low genomic risk, as determined by this test, do very well without chemotherapy. The study also found that for women with tumors that carry intermediate risk, either by the genomic assay or by traditional factors, a favorable MammaPrint result again confers a good prognosis, though it remains unclear whether chemotherapy might still eke out some small benefit.

Collectively, these studies confirm that we are now in the “genomic area” of tailored therapy for breast cancer. It will become routine in the future for all breast cancers to undergo genomic sequencing. For now, genomic test results are important for making better treatment decisions in ER positive, stage 1 or 2 breast cancer, which is the most common presentation of breast cancer in the US accounting for over 150,000 cases every year.

This is a beautiful situation where we have been able to use advanced diagnostic tools and precision medicine to make better and more tailored decisions for patients with a very common cancer. As a result, tens of thousands of women are spared chemotherapy every year.

Finally, we have too often under-invested in diagnostic tests while over-spending on drugs. These genomic tests are expensive, but their price pales in comparison to the cost of chemotherapy. By allowing us to avoid toxic and costly treatments when not needed, diagnostic tests more than prove their value.

Harold J. Burstein, M.D is affiliated with Dana-Farber Cancer Institute, Harvard Medical School and is Chair of the Cancer Communications Committee and Breast Cancer Expert at the American Society of Clinical Oncology.  


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