Electron Intraoperative Radiotherapy Associated With Increased IBTR Rates for Early-Stage Breast Cancer

Matthew Fowler

The long-term equivalence trial examined the rates of ipsilateral breast tumor recurrence for patients receiving electron intraoperative radiotherapy and whole-breast irradiation at 5-, 10-, and 15-year follow-up times.

New results from the phase 3 ELIOT trial (NCT01849133) confirmed previously reported long-term recurrence rates and found no difference in overall survival between patients treated with electron intraoperative radiotherapy (ELIOT) versus whole-breast irradiation (WBI), suggesting that latter may be offered to specific patients at low-risk of ipsilateral breast tumor recurrence (IBTR), according to data published in Lancet Oncology.1

The updated analysis of the single-center, randomized trial continued to show that patients with early-stage breast cancer who received accelerated partial breast irradiation (APBI) with ELIOT had a higher rate of IBTR than patients who received WBI.

“This long-term analysis of the ELIOT study shows a higher rate of IBTR in the ELIOT group than in the WBI group at longer follow-up, supporting the results of the previous analysis, without any differences in distant relapse and overall survival between the groups,” wrote the investigators.

The first results of this trial were determined in 2013 after a median follow-up of 5.8 years, showing that patients in the ELIOT group experienced a higher rate of IBTR than patients in the WBI group.2 These corresponding data compare survival outcomes between the groups at the 5-, 10-, and 15-year follow-up mark.

The trial population included 1305 patients randomly assigned to either the WBI group (n = 654) or the ELIOT group (n = 651).

The 5-year IBTR rate was 4.2% (95% CI, 2.8%-5.9%) in the ELIOT group compared with 0.5% (95% CI, 0.1%-1.3%) in the WBI group. The 10-year IBTR rates were 8.1% (95% CI, 6.1%-10.3%) and 1.1% (95% CI, 0.5%-2.2%) in the ELIOT and WBI groups, respectively. The 15-year rate for patients in the ELIOT group was 12.6% (95% CI, 9.8%-15.9%) and was 2.4% (95% CI, 1.4%-4.0%) for patients in the WBI group.

The final follow-up on March 11, 2019 showed 193 patient deaths from any cause without a significant difference between the ELIOT group (98 deaths) and WBI group (95 deaths; HR, 1.03; 95% CI, 0.77-1.36; P = .85).

For patients in the ELIOT group, the overall survival (OS) rates were 96.8% (95% CI, 95.1%-97.9%), 90.7% (95% CI, 88.2%-92.7%), and 83.4% (95% CI, 79.7%-86.4%) at 5, 10, and 15 years, respectively. Comparatively, the OS rates for patients in the WBI group were 96.8% (95% CI, 95.1%-97.9%) at 5 years, 92.7% (95% CI, 90.4%-94.4%) at 10 years, and 82.4% (95% CI, 78.5%-85.6%) at 15 years.

“This trial, which to our knowledge has the longest follow-up of all APBI and intraoperative radiotherapy trials, shows that the rate of local and regional recurrences in women with early-stage breast cancer is significantly higher after ELIOT than after WBI (with very low rates of local recurrence after WBI), but that these increased recurrences have no effect on the important outcomes of overall survival or distant metastatic spread at 10 and 15 years,” wrote the investigators.

The primary end point of the research was the occurrence of IBTR, with the main secondary end point focusing on OS.

The lack of long-term toxicity data was the main limitation of this research, according to the investigative team. Regardless, there were no differences observed in mortality between the treatment groups.

More, collecting long-term data was a limitation, as many patients lived in distant regions and were not followed-up with at the European Institute of Oncology after the 5-year follow-up period.

Future trials are recommended to investigative the potential for certain patients to avoid radiotherapy moving forward.

Reference:

1. Orecchia R, Veronesi U, Maisonneuve P, et al. Intraoperative irradiation for early breast cancer (ELIOT): long-term recurrence and survival outcomes from a single-centre, randomised, phase 3 equivalence trial. Lancet Oncol. 2021;22(5):597-608. doi:10.1016/S1470-2045(21)00080-2

2. Veronesi U, Orecchia R, Maisonneuve P, et al. Intraoperative radiotherapy versus external radiotherapy for early breast cancer (ELIOT): a randomised controlled equivalence trial. Lancet Oncol. 2013;14(13):1269-1277. doi:10.1016/S1470-2045(13)70497-2