In a retrospective analysis reported in the International Journal of Radiation Oncology • Biology • Physics, Jaoude et al found that a radiation boost did not reduce the risk of local recurrence among women with HER2-positive breast cancer receiving breast-conserving surgery, whole-breast irradiation, and adjuvant trastuzumab in the phase III HERA trial. 

The HERA trial, which now has median follow-up of 11 years, established the benefit of adjuvant trastuzumab in patients with HER2-positive breast cancer.

Study Details

The analysis included data from 1,082 women in the HERA trial (n = 5,099) who received breast-conserving surgery, whole-breast irradiation, and adjuvant trastuzumab. Among this population, 441 patients received an additional radiation boost to the primary tumor bed and 641 received no boost.

Patients randomly assigned to the observation arm (those who did not receive trastuzumab), those who did not receive radiotherapy, and those who underwent mastectomy were excluded from the analysis. The primary outcome measure for the analysis was local recurrence.

Key Findings

At median follow-up of 11 years, local recurrence was observed in 7.21% of all patients included in the analysis. Rates were 6.35% in the boost group vs 7.80% in the no-boost group (absolute reduction = 1.4%; P = .33). On multivariate analysis, the adjusted hazard ratio [HR] for boost vs no boost was 0.8 (P = .30).

Patients younger than age 40 had a higher risk for local recurrence vs older women. Among women younger than 40, local recurrence occurred in 8.89% of the boost group vs 11.11% of the no-boost group (adjusted HR = 1.0, P = .92). Rates among patients age 40 or older were 5.70% vs 6.99% (adjusted HR = 0.7, P = .29).

No significant differences in local recurrence rates were identified according to hormone receptor status. Among patients with estrogen receptor (ER)- and progesterone receptor (PR)-negative disease, rates were 8.95% the boost group vs 8.05% in the no-boost group (adjusted HR = 1.0, P = .98). Among patients with ER- or PR-positive disease, rates were 4.38% with a boost and 7.55% without a boost (adjusted HR = 0.6, P = .11).

The investigators concluded, “[Patients with] HER2-positive breast cancer treated with breast-conserving surgery, whole-breast radiation, and trastuzumab have excellent local control. Delivery of an additional radiation boost in this patient population was not shown to improve local control. Future studies are needed to identify subgroups of HER2-positive patients who derive a clinically relevant benefit from radiation boost.”

Youssef H. Zeidan, MD, PhD, of the Department of Radiation Oncology, American University of Beirut Medical Center, is the corresponding author for the International Journal of Radiation Oncology • Biology • Physics article.

Disclosure: For full disclosures of the study authors, visit redjournal.org.