Use of adjuvant chemotherapy in hormone receptor‑positive breast cancer patients with or without the 21‑gene expression assay

Abstract

Purpose We assessed the use of chemotherapy in breast cancer patients to investigate the factors that changed trends in chemotherapy following the adoption of the 21-gene expression assay in tumor genomic profiling.

Methods Our study used 2033 patients from the National Cancer Center in Korea diagnosed with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer (tumor size of 0.5 cm or larger and 0–3 node metastases) from 2010 to 2015. We analyzed use of the 21-gene expression assay, changes in frequency of adjuvant chemotherapy use, and clinicopathological factors related to adjuvant chemotherapy to assess the impact of the 21-gene expression assay.

Results Adjuvant chemotherapy use declined from 33.33% (2011) to 13.59% (2015) [relative risk (RR), 0.71; 95% CI 0.56–0.89; ptrend = 0.004] in patients with 21-gene expression assay data. Among patients without assay data, adjuvant chemotherapy use decreased from 76.79 to 40.17% between 2010 and 2015 (RR 0.87; 95% CI 0.84–0.91; ptrend < 0.001), especially for patients with node-negative/micrometastasis (RR 0.85; 95% CI 0.81–0.89; ptrend < 0.001). The frequency of adjuvant chemotherapy was significantly decreased after introduction of the 21-gene expression assay (p < 0.001). Tumor size (p < 0.001), progesterone receptor (PgR) status (p = 0.001), and proliferation index (Ki-67) levels (p < 0.001) were important factors for chemotherapy decision-making in node-negative/micrometastasis patients who did not undergo the assay.

Conclusions For HR-positive, HER2-negative breast cancer patients with 0–1 node metastases, chemotherapy use declined significantly after the adoption of the 21-gene assay. PgR status and Ki-67 were useful for chemotherapy decision-making in cases without the 21-gene assay.