A new test may help to identify breast cancer patients with the lowest risk of death, therefore helping them to avoid unnecessarily aggressive treatment.

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Could a new test accurately predict survival rates for breast cancer patients who fall within a specific category?

Breast cancer is currently the most common form of cancer in women, regardless of race or ethnicity. Overall, breast cancer ranks as the second leading cause of cancer-related death among women.

Breast cancer mortality trends have declined significantly during the past decade, largely due to public awareness campaigns that focus on early detection and prevention. However, early screening can also result in some patients being over-treated.

Screening can detect very low risk, non-life-threatening tumors, and this can sometimes lead to unnecessarily aggressive treatment. The problem is often exacerbated because the cancer can recur within 5 years and because there had been no tools able to accurately predict which patients were the likeliest to survive over that period.

But now this could change, as researchers from the University of California, San Francisco (UCSF) - in collaboration with scientists from various universities across Sweden - have found that a molecular test can help to predict which breast cancer patients will have the lowest risk of death.

The lead author of the study is Dr. Laura J. Esserman, a breast cancer specialist and surgeon with UCHealth. The findings were published in the journal JAMA Oncology.

Examining the MammaPrint test

Dr. Esserman and team set out to examine the potential of an already existing test to determine which tumors were "indolent, or slow-growing." This test is called MammaPrint, and it was approved by the United States Food and Drug Administration (FDA) in 2007.

The test was designed by study co-author and UCSF researcher Laura van 't Veer. She is also a co-founder of Agendia, the company that produces the test. For this research, Agendia analyzed tumor samples free of charge.

MammaPrint is a 70-gene signature test that is widely used to determine which patients do not need adjuvant chemotherapy.

As the authors of the new study report, in 2016, this test indicated that almost half of the breast cancer patients that were considered "early stage," but who had all the traditional signs of being at a high risk of recurrence, could, in fact, do without chemotherapy. This evaluation was based on the biological composition of the tumors.

For the new research, Dr. Esserman and colleagues decided to use this test to evaluate the risk of breast cancer recurrence over a period of 20 years after being diagnosed.

To do so, they examined patients from the Stockholm breast cancer study group, all of whom had been clinically followed for decades as part of a clinical trial for the tumor-suppressing drug tamoxifen.

The trial comprised 1,780 patients whose breast cancer had not spread to their lymph nodes. All the women had had a mastectomy or a lumpectomy and undergone radiation treatment. Dr. Esserman and colleagues used the tissue to calculate the MammaPrint risk scoring for 652 women.

'Excellent' prognosis for some patients

The 70-gene signature test identified 42 percent of the patients as being at high risk of recurrence, and 58 percent as being at low risk. Dr. Esserman and team found that 95 percent of those deemed low risk survived for 5 years, but also that many of them died later from breast cancer.

However, the test also categorized 15 percent of the patients as "ultralow risk." These patients had "excellent long-term survival," regardless of whether or not they took tamoxifen for 2 years.

The 20-year breast cancer-specific survival rate among ultralow risk patients was 97 percent among those who took tamoxifen, compared with 94 percent in the control group.

"This is an important step forward for personalizing care for women with breast cancer. We can now test small node-negative breast cancers, and if they are in the ultralow risk category, we can tell women that they are highly unlikely to die of their cancers and do not need aggressive treatment, including radiation after lumpectomy."

Dr. Laura J. Esserman

The authors also note that, with early screening, as many as 25 percent of postmenopausal women may fall into the ultralow risk category.

"There are breast cancers that pose little or no systemic risk," Dr. Esserman explains. "Women who have a tumor that is classified as ultralow risk by 70-gene signature can be reassured that their long-term outcome is expected to be excellent, with or without endocrine therapy."

"Having a test that accurately identifies a population of women, who have very little risk to begin with, should be welcomed by patients and clinicians alike."

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