TARGIT-C(Consolidation) Prospective Phase IV Study of IORT in Patients With Small Breast Cancer

This prospective, multicentric single arm phase IV study is based on the protocol of the international TARGIT-A and TARGIT-E study.

Patients ≥ 50 years with small, low-risk breast cancer who are operated but not irradiated show local relapse rates around 6% after 5 years. With adjuvant whole breast radiotherapy (WBRT) the local relapse rate drops to under 1% after 5 years under Tamoxifen (4).

It has been demonstrated (6, 9, 10) that the efficacy of radiation of the tumor bed only in a selected group can be non-inferior to WBRT.

The TARGIT C study should confirm the efficacy of a single dose of intraoperative radiotherapy (IORT) in a well selected group of patients with small breast cancer and absence of risk factors. In presence of risk factors postoperative WBRT will be added to complete the radiotherapeutic treatment according to international guidelines.

Endpoints are the local relapse rate (within 2 cm of the tumor bed), ipsilateral relapse, cancer-specific and overall survival and contralateral breast cancer as well as documentation of quality of life and cosmetic outcome.

The expected local relapse rates are 0.825/1.375% after 3/5 years, respectively. Discontinuation of the trial is scheduled if rates of local relapse rates rise to 1.55/2.4/4% after 1/3/5 years. Power calculations result in 387 patients with a calculated dropout and loss to follow-up rate of 10%, an alpha of 0.05 and a beta of 0.10. There will be only a pre-pathology stratum.

It is a pragmatic trial in which each participating centre has the option to modify entry criteria and criteria for WBRT according to this core protocol after consultation with the steering committee and local ethics committee (e.g. size, free margins). Only centers with access to the Intrabeam® system (Carl Zeiss) can recruit patients into the trial.