The Effect of Adjuvant Treatment in Small Node-negative HER2-positive Breast Cancer: Which Subgroup Will Benefit?

We conducted this study to evaluate whether patients with T1a/b, node-negative (N^-), human epidermal growth factor receptor 2-positive (HER2⁺) breast cancers benefited from adjuvant therapy, and explored better treatment strategies for these patients.

Patients with T1a/b, N^-, HER2⁺ breast cancers during 2000 through 2004 were identified from the Surveillance, Epidemiology, and End Results (SEER) database. The Gray test was used to evaluate breast cancer-specific death (BCSD) and non-BCSD. To identify patients more suitable for chemotherapy, subgroup analyses were conducted according to tumor size and estrogen receptor (ER) status, and plots of hazard rate of death (HRD) were drawn to present the changes of BCSD.

A total of 2940 patients with T1a/b, N^-, HER2⁺ breast cancers were included; more patients in the T1b group received chemotherapy compared with the T1a group (65.18% vs. 29.30%; P < .001). Patients receiving chemotherapy did not benefit from it (5-year incidences of BCSD: 1.00% in the non-chemotherapy group vs. 1.18% in the chemotherapy group; P = .853). Compared with those in the T1a group, patients in the T1b group had similar prognosis (P = .532), whereas ER status was significantly associated with survival (P = .048). HRD had a peak in years 2 to 5, which was more obvious in the ER^- group.

Chemotherapy, which is mainly decided by tumor size, fails to render survival benefits for patients with T1a/b, N^-, HER2⁺ breast cancers. ER status, rather than tumor size, is important for clinicians to make adjuvant treatment decisions. The peak of BCSD occurs 2 to 5 years after diagnosis, and an at least 5-year follow-up is recommended for these patients.