NEW YORK – Researchers at the MD Anderson Cancer Center, Loyola University Chicago Stritch School of Medicine, and elsewhere have determined that a breast cancer recurrence score provided by the Genomic Health 21-gene expression assay OncotypeDX may provide valuable prognostic information on locoregional disease recurrence that may aid in decision-making about radiotherapy for postmenopausal women with node-positive, estrogen receptor- or progesterone receptor-positive breast cancer.
In a study published on Thursday in JAMA Oncology, the researchers reported their retrospective analysis of a cohort of 316 women with breast cancer who were participants in the Southwest Oncology Group (SWOG) S8814 trial — a Phase III randomized clinical trial of postmenopausal women with ER/PR-positive, node-positive breast cancer treated with tamoxifen alone, chemotherapy followed by tamoxifen, or concurrent tamoxifen and chemotherapy.
Of the 316 women in the cohort, the researchers recorded seven events (5.8 percent) of locoregional recurrence (LRR) in the 121 patients with a low recurrence score. In contrast, they recorded 27 LRR events (13.8 percent) among the 195 patients with intermediate or high recurrence scores. The estimated 10-year cumulative incidence rates were 9.7 percent for those with a low recurrence score and 16.5 percent for the group with intermediate or high recurrence scores.
Among the 252 patients who had a mastectomy without radiotherapy, the researchers saw significant differences in the 10-year actuarial LRR rates: 7.7 percent for the low recurrence score group compared to 16.8 percent for the intermediate or high recurrence score group.
"A multivariable model controlling for randomized treatment, number of positive nodes, and surgical type showed that a higher recurrence score was prognostic for LRR," the authors wrote. "In a subset analysis of patients with a mastectomy and one to three involved nodes who did not receive radiation therapy, the group with a low recurrence score had a 1.5 percent rate of LRR, whereas the group with an intermediate or high recurrence score had a 11.1 percent LRR."
Although genomic data have not been routinely incorporated into local therapy decisions for patients with breast cancer and positive lymph nodes, this study demonstrated that recurrence score could be used as an independent prognostic factor for LRR for postmenopausal patients with node-positive, ER/PR-positive, nonmetastatic breast cancer, the researchers added.
Specifically, the findings suggest that radiotherapy should remain as a standard treatment in patients with any recurrence score and four or more positive nodes, they said. The findings also suggest the possibility of omitting radiotherapy in patients with low recurrence score and one to three positive nodes.
"We believe these data support using recurrence scores — along with standard clinical factors like age or tumor size — to determine risk of recurrence and radiotherapy decisions for patients," Wendy Woodward, the study's first authors and chief of the clinical breast radiotherapy service at MD Anderson, said in a statement. "Our findings are clearly limited, as we had some small patient numbers and looked at data retrospectively. But these results provide additional evidence of the value of this test in node-positive patients. And they suggest it might be possible to skip radiation in patients with low recurrence scores and one to three cancer-positive nodes."
Woodward further noted that the question of whether it's possible to skip radiation treatment in this particular patient population is a question now being tested in the Regional Radiotherapy in Biomarker Low Risk Node Positive Breast Cancer (TAILOR RT) trial, which is currently being conducted by SWOG and several collaborators.
"There are large clinical trials going on looking at radiation care for breast cancer patients, like TAILOR RT, and I encourage people to enroll," Woodward said. "The more data we have, the more we'll know how to use this new precision medicine tool."