Author: By Lynda Williams, Senior medwireNews Reporter
medwireNews: Postmenopausal women with early hormone receptor-positive, HER2-negative breast cancer and a low genomic risk of recurrence may not require adjuvant chemotherapy, suggest the SWOG S1007 RxPONDER investigators.
The first findings from the phase III trial were presented during the 2020 San Antonio Breast Cancer Symposium by Kevin Kalinsky, from the Winship Cancer Institute of Emory University in Atlanta, Georgia, USA.
He explained that SWOG S1700 was a randomised study comparing taxane- or anthracycline-based chemotherapy followed by endocrine therapy (n=2509) versus endocrine therapy only (n=2506) for women with between one and three positive lymph nodes who had scored 25 or less out of a possible 100 on the genome-based Oncotype Dx recurrence score (RS) from a primary tumour sample.
Primary interaction analysis indicated that the RS did not significantly predict the relative benefit of chemotherapy with regard to invasive disease-free survival (IDFS), so that patients with a lower RS did not have a smaller benefit with chemotherapy than those with a higher RS, the presenter said.
However, chemotherapy use was independently prognostic for IDFS, so that patients given chemoendocrine therapy had a significantly better 5-year rate of IDFS than those given only endocrine therapy (92.4 vs 91.0%, hazard ratio [HR]=0.81).
Moreover, further analysis identified a significant interaction between use of chemotherapy and menopausal status, continued Kevin Kalinsky.
Two-thirds of the participants in the study were postmenopausal (n=3350) and there was no significant difference in the 5-year rate of IDFS for women who received chemoendocrine therapy and those given endocrine therapy, at 91.6% versus 91.9%.
But among the 1665 premenopausal patients, the 5-year IDFS rate was 94.2% for women who received chemoendocrine therapy and 89.0% for those who received only endocrine therapy, giving a significant adjusted HR of 0.54 in favour of chemotherapy use.
While distant recurrence as a first event occurred in a comparable proportion of postmenopausal women given chemoendocrine and endocrine therapy (2.3 vs 2.6%), premenopausal women given chemoendocrine therapy were less likely to have distant recurrence as a first recurrence than those using only endocrine therapy (3.1 vs 6.0%), although the presenter said events were too few to be able to comment on the statistical significance of this finding.
Forest plot analysis indicated that premenopausal women derived a benefit from chemoendocrine therapy across subgroups of age, tumour grade or size, number of positive lymph nodes and recurrence score (14–25 vs 0–13), albeit with some wide confidence intervals, whereas no advantage with chemotherapy was identified in the postmenopausal group, reported Kevin Kalinsky.
And landmark exploratory analysis among premenopausal women given only endocrine therapy found no significant difference in IDFS for the 126 patients who were receiving ovarian suppression at 6 months into the trial and the 647 patients who were not.
Overall survival stratified by menopausal status did not significantly differ at 5 years in the treatment arms of the postmenopausal patients given chemoendocrine and endocrine-only treatment (96.2 vs 96.1%) but had a 1.3 percentage point difference between the premenopausal treatment groups (98.6 vs 97.3%), with a significant adjusted HR of 0.47.
“Postmenopausal women with positive nodes and recurrence score 0–25 can likely safely forgo adjuvant chemotherapy without compromising IDFS”, the presenter concluded.
On the other hand, “premenopausal women with positive nodes and RS 0–25 likely benefit significantly from chemotherapy”, he emphasized.
Abstract GS3-00. Kalinsky K, Barlow WE, Meric-Bernstam F, et al. First results from a phase III randomized clinical trial of standard adjuvant endocrine therapy (ET) +/- chemotherapy (CT) in patients (pts) with 1–3 positive nodes, hormone receptor-positive (HR+) and HER2-negative (HER2-) breast cancer (BC) with recurrence score (RS) ≤25: SWOG S1007 (RxPONDER). 2020 San Antonio Breast Cancer Symposium; 8–11 December.
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