Short course hypofractionated whole breast irradiation after conservative surgery: a single institution phase II study.

Background: To assess the oncologic outcomes of hypofractionated whole breast irradiation (Hypo-WBI).

Methods: Eligible patients had undergone breast conservative surgery for early breast cancer (pTis-2) and none/limited nodal involvement. Hypo-WBI consisted of 34 Gy in 10 daily fractions over 2 weeks to the whole breast three-dimensional conformal radiotherapy (3DCRT), followed by a single fraction of 8 Gy to the tumor bed after 1 week (electrons). Primary endpoint is freedom from ipsilateral breast tumor recurrence (IBTR). Minimum follow up for living & event-free patients is 3 yrs.; median follow up time of the whole analyzed patient population is 5.4 yrs. (range: 1.8-11.4 yrs).

Results: Two hundred fifty-one patients were accrued from 2004 to 2013. All patients underwent local excision of the primary tumor to negative margins. Four patients failed in the ipsilateral breast after a median time of 3.2 years (range: 1.7-5.7 yrs) for a 5-year IBTR-free survival of 98.7% (95%CI: 97.3%-100%). IBTR-free survival was significantly higher for patients with invasive cancer than for patients with intraductal carcinoma (p = 0.036). Within patients with invasive tumors, no clear trends or associations were detected between IBTR and age, grading, molecular subtype, pT or pN stage. At 5 years, the actuarial rates of GR2 fibrosis and GR2+ teleangectasia are 2.4% (95%CI: 0-6.5%) and 7.1% (95%CI: 0.4-13.7%), respectively. Cosmesis was scored as excellent/good by ≈95% of patients and ≈60% of clinicians.

Conclusions: Hypo-WBI in 3 weeks allows excellent oncologic outcomes for invasive breast cancer after conservative surgery. Patients with intraductal carcinoma should be treated with Hypo-WBI only within a controlled study.

Trial Registration: IRE-IFO Ethical and Scientific Committee (cod. RS61/04).