NEW YORK (GenomeWeb) – In a study published in the latest issue of the New England Journal of Medicine, an international team led by investigators in the US validated Genomic Health's Oncotype DX as a means to stratify treatment in a prospective trial of women with a relatively low risk breast cancer subtype.
The researchers used the assay — based on a 21-gene expression profile — to generate recurrence risk scores for nearly 10,300 women with hormone-receptor positive, HER2-negative, axillary node-negative invasive breast cancer.
The 1,626 women with the lowest recurrence risk scores were treated using endocrine therapy only, while the remaining women received both endocrine therapy and chemotherapy. Five years after treatment, the team saw high rates of invasive disease-free survival, recurrence-free survival, and an overall survival rate of 98 percent in that treatment group.
"[T]his prospective study involving uniformly treated patients with hormone receptor-positive, HER2-negative, axillary node-negative breast cancer supports the clinical validity of the 21-gene assay in identifying patients who may be safely spared adjuvant chemotherapy," senior author Joseph Sparano, an oncology researcher at Montefiore Medical Center, and colleagues wrote.
Past studies suggest women with estrogen receptor-positive breast cancer have recurrence-free survival rates of roughly 85 percent following endocrine therapy, the team explained.
Both endocrine and adjuvant chemotherapy are generally used as a means of curbing recurrence in another 5 percent or so of cases, though the chemotherapy step is presumed to be unnecessary for many of the women with this breast cancer subtype.
"Many patients with estrogen receptor-positive breast cancer would … be overtreated with chemotherapy on the basis of clinicopathologic features alone," the researchers wrote, "since most would have been adequately treated with endocrine therapy alone."
As part of a clinical trial known as the Trial Assigning Individualized Options for Treatment, or TAILORx, they decided to prospectively test the Oncotype DX Recurrence Score assay's ability to predict survival benefits from adjuvant chemotherapy, using Oncotype DX to gauge recurrence risk in 10,253 HER2-negative breast cancer cases enrolled between spring 2006 and fall 2010.
The cancers were axillary node-negative, but positive for estrogen receptor and/or progesterone receptor expression and affected women between the ages of 18 and 75 years.
On a recurrence risk scale of zero to 100, the team found that 1,626 women who were eligible to participate in the trial fell into the lowest risk group, with scores under 10. Another 6,897 had scores between 11 and 25 and were classified in the mid-range risk group, while 1,730 cases had higher recurrence risk, coming in at 26 or higher recurrence scores.
All but six of the patients in the lowest risk group were treated with endocrine therapy alone — treatments such as aromatase inhibition, tamoxifen, or tamoxifen followed by another endocrine therapy.
One of the six individuals who received adjuvant chemotherapy experienced recurrence, the researchers reported, and 88 of the individuals in the low-risk group had invasive cancer or death in the five years following treatment.
In the low-risk group as a whole, though, the researchers saw recurrence-free survival rates of nearly 99 percent over five years and an overall five-year survival rate of 98 percent. Just shy of 94 percent of women in the low-risk group remained free from invasive disease after five years.
The team noted that similar studies by other groups are underway to test the clinical validity of foregoing adjuvant chemotherapy in individuals with recurrence scores as high as 25.
GenomeWeb has more information on the TAILORx findings and remaining treatment questions for women in the intermediate recurrence risk group in a premium article published in September.