Postmenopausal patients with "ultralow-risk" breast cancers may be able to forgo standard endocrine treatment with tamoxifen, which is routinely prescribed after surgery for many patients.
The new findings come from a long-term follow-up of patients who were retrospectively tested with the Mammaprint 70-gene panel. The findings were published online June 29 in JAMA Oncology.
In the study, patients whose tumors scored under the ultralow-risk threshold on the Mammaprint panel and who did not receive tamoxifen had an "exceedingly low" risk for death from breast cancer during 20 years of follow-up, report the investigators, led by Laura Esserman, MD, of the Helen Diller Family Comprehensive Cancer Center at the University of California, San Francisco (UCSF).
"This is an exciting advance because approximately 20% to 25% of tumors diagnosed today may be ultralow risk," said Dr Esserman in a press statement.
The ability to identify patients with ultralow-risk disease can allow clinicians to make bold recommendations, suggested Dr Esserman.
"You can really say to someone, 'You're not going to die of this disease. And we don't have to be aggressive up front and treat you with everything," she said in an article posted on the npr.org website.
Dr Esserman provided Medscape Medical News with an example of how she uses the Mammaprint test in her practice. An older patient with a number of comorbidities was "very afraid to stop her hormone therapy that was also causing her significant difficulty walking up stairs. Her tumor was ultralow. I was able to reassure her that she could safely stop the hormone therapy," she said.
The concept of ultralow-risk breast cancer has been talked about for the past decade or so, said Dr Esserman, but this is the first evidence that it is possible to run a diagnostic test at the time of diagnosis to identify a breast cancer as being associated with ultralow risk.
The new study from Dr Esserman and colleagues is a secondary analysis of the Stockholm Tamoxifen clinical trial (STO-3), which enrolled patients from 1976 to 1990 in Sweden.
The trial included patients with small (≤3 cm), hormone-receptor-positive early-stage breast cancers. Such patients are typically treated with endocrine therapy, such as tamoxifen, after the tumor is surgically removed.
In the trial, after first undergoing surgery, half of the patients were treated with tamoxifen, and the other half received no antiestrogen therapy. Most of the women (79%) received mastectomies. For all participants, tumors were detected clinically, because the trial took place before screening mammography was widely used in Sweden.
In the new analysis, Dr Esserman and coinvestigators used the Swedish trial's archived tumor blocks to perform retrospective risk assessments with the Mammaprint assay among 652 participants with node-negative disease.
The Mammaprint panel identified 377 women (58%) as being at low risk and 275 (42%) as being at high risk. Such binary information is typically used by clinicians to help decide about using adjuvant chemotherapy. Indeed, a huge European trial has shown that use of the Mammaprint test results in de-escalation of chemotherapy for patients with early-stage breast cancer.