Breast cancer-specific survival in patients with HER2-positive, node-negative T1a and T1b breast cancer

Purpose: There is limited data on prognosis of node-negative (N0), HER2-positive (HER2+) small breast cancers. We evaluated breast cancer-specific survival (BCSS) among women diagnosed with T1a/T1b, N0 tumors in California between 2000–2004 and 2005–2012, eras before and after approval of adjuvant trastuzumab. Patients and Methods: 45,346 women diagnosed with T1a/b, N0 tumors between January 1, 2000 and December 31, 2012 were identified in the California Cancer Registry (CCR); approximately 10% were HER2 +, and 80% hormone receptor positive (ER and/or PR+). Primary outcome was BCSS, analyzed in 2000–2004 and 2005–2012. Multivariable Cox proportional hazards regression was used to calculate hazard ratios and 95% confidence intervals for mortality, and separately conducted for hormone receptor positive and negative tumors. Kaplan-Meier curves compared BCSS by HER2 status. Results: While BCSS in this cohort exceeded 90%, a significantly higher hazard of breast cancer death was observed in women with HER2+ tumors in the 2000–2004 era. There was no difference in outcomes between T1a and T1b tumors. Women with ER/PR+ tumors had lower hazards of death in both eras, but HER2+ tumors were associated with a higher hazard of death in the 2000–2004 era. Among women with hormone receptor negative tumors, HER2 positive disease was associated with a lower hazard of death in the 2005–2012 era. Conclusion: Within this large cohort of T1a/b N0 breast cancers from the CCR, HER2+ tumors were associated with a significantly worse BCSS in the era before adjuvant trastuzumab. A balanced discussion regarding HER2-directed therapies is needed between patient and clinician.