Role of Chemotherapy in Postmenopausal Women with Node Positive Early Breast Cancer

SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (13%) will develop invasive breast cancer during their lifetime. Approximately 276,480 new cases of invasive female breast cancer were diagnosed in 2020 and about 42,170 women died of the disease. Approximately 25% of patients with Hormone Receptor (HR)-positive, HER2-negative early breast cancer have metastatic lymph node involvement and two third of these patients are postmenopausal. Majority of these patients currently receive chemotherapy. The Oncotype DX breast cancer assay, is a multigene genomic test that analyzes the activity of a group of 21 genes and is able to predict the risk of breast cancer recurrence and likelihood of benefit from systemic chemotherapy, following surgery, in women with early stage breast cancer. Chemotherapy recommendations for early stage, HR-positive, HER-negative, early stage breast cancer patients, are often made based on tumor size, grade, ImmunoHistoChemical (IHC) markers such as Ki-67, nodal status and Oncotype DX Recurrence Score (RS) assay.

In the ground-breaking TAILORx (Trial Assigning Individualized Options for Treatment) study which enrolled 10,273 patients with HR-positive, HER2-negative, axillary node-negative breast cancer, patients were divided into three groups based on their Recurrence Score. Patient with Intermediate Recurrence Score of 11-25 were randomly assigned to receive endocrine therapy alone or endocrine therapy and adjuvant chemotherapy. There was no benefit noted from adding chemotherapy to endocrine therapy, for women older than 50 years in this Intermediate RS group, suggesting that a significant percentage of women with node-negative breast cancer do not achieve substantial benefit from chemotherapy. For women 50 years old or younger who received chemotherapy and had a Recurrence Score of 16 to 25, there was a lower rate of distant recurrence and the risk of recurrence and benefit of chemotherapy was further influenced by the tumor size and grade. Whether the results of TAILORx can be extrapolated to women with node-positive breast cancer has remained unclear. It is estimated that approximately 85% of women with node-positive disease have Recurrence Score results of 0-25.

The RxPONDER trial was designed to determine the benefit of chemotherapy, in patients who had a Recurrence Score of 0-25. This trial did not include pre and postmenopausal women with Recurrence Score results 26-100 based on previously published studies suggesting that this patient group benefited from chemotherapy. SWOG S1007 (RxPONDER) is an multicenter, international, prospective, randomized, Phase III trial, in which patients with HR-positive, HER2-negative breast cancer with 1-3 positive axillary lymph nodes were included, to determine which patients would benefit from chemotherapy and which patients could safely avoid it. In this study, a total of 5083 HR-positive, HER2-negative breast cancer patients with 1-3 positive lymph nodes and Oncotype DX Recurrence Score of less than 25 were randomly assigned 1:1 to receive chemotherapy plus endocrine therapy or endocrine therapy alone. Approximately two-thirds of patients were postmenopausal and one-third were premenopausal and had no contraindications to taxane and/or anthracycline based chemotherapy. Patients were stratified by Recurrence Score (0-13 versus 14-25), menopausal status, and axillary nodal dissection versus sentinel node biopsy. The Primary endpoint was Invasive Disease Free Survival (IDFS), defined as local, regional, or distant recurrence, any second invasive cancer, or death from any cause, and whether the effect depended on the Recurrence Score. Secondary endpoints included Overall Survival (OS).

At a median follow up of 5.1 years, there was no association noted between Recurrence Score (RS) values and chemotherapy benefit for the entire study population (P=0.30). However, a prespecified analysis did show a significant association between chemotherapy benefit and menopausal status. Premenopausal women (N=1665) with an RS between 0 and 25 had an IDFS benefit with the addition of chemotherapy to endocrine therapy compared with endocrine therapy alone (94.2% versus 89%, HR=0.54; P=0.0004). This absolute 5.2% benefit in the premenopausal subset was highly significant. The relative risk reduction with the addition of chemotherapy to endocrine therapy for the two RS risk groups 0-13 and 14-25 was consistent in the premenopausal population, with an overall Hazard Ratio of 0.54. The absolute benefit was numerically higher in those with RS 14-25. Consistent benefit was again noted regardless of number of involved lymph nodes, although there was slight variation in the absolute benefit. Postmenopausal women (N=3350) did not benefit with the addition of chemotherapy to endocrine therapy when compared endocrine therapy alone, regardless of Recurrence Score (91.9% versus 91.6%, HR=0.97; P=0.82). Chemotherapy also improved Overall Survival in the premenopausal cohort, although the follow up is limited.

It was concluded from this practice-changing outcomes that postmenopausal women with HR-positive, HER2-negative breast cancer with 1-3 positive nodes and Oncotype DX Recurrence Score of 25 or less can safely avoid receiving adjuvant chemotherapy, whereas premenopausal patients with 1-3 positive nodes and a Recurrence Score of 25 or less should consider adjuvant chemotherapy. The authors added that these finding demonstrate that the great majority of postmenopausal women can be spared unnecessary chemotherapy and receive only endocrine therapy.

First results from a phase III randomized clinical trial of standard adjuvant endocrine therapy ± chemotherapy in patients with 1-3 positive nodes, hormone receptor-positive and HER2-negative breast cancer with recurrence scores ≤ 25: SWOG S1007 (RxPONDER). Kalinsky K, Barlow WE, Meric-Bernstam F, et al. 2020 San Antonio Breast Cancer Symposium. Presented December 10, 2020. Abstract GS3-00.