SAN ANTONIO – Accelerated partial breast irradiation (APBI) using an interstitial multicatheter brachytherapy method is as effective as whole breast irradiation (WBI) at preventing local disease recurrence 5 years after surgery for early breast cancer, according to the long-term results of a large European randomized phase III trial.
The cumulative incidence of local recurrence was 1.44% in the women who received ABPI and 0.92% in the women who received conventional WBI followed by a further boost of radiation to the tumor-bed in the GEC-ESTRO (Groupe Européen de Curiethérapie of European Society for Radiotherapy and Oncology) trial. The 0.52% difference between the two types of radiation therapy was not statistically significant and was within the 3% margin set for noninferiority.
Results of the trial also showed similarly high, and not statistically different, 5-year disease-free (95.03% vs. 94.4%) and overall survival (97.3% vs. 95.5%) for APBI and WBI.
Dr. Vratislav Strnad
“This is the first phase III study proving noninferiority of APBI in comparison to whole breast irradiation for selected early stage breast cancer patients,” said Dr. Vratislav Strnad of University Hospital Erlangen, Germany, during a press briefing at the annual meeting of the American Society for Radiation Oncology.
Dr. Strnad added, “Based on our results, APBI using multicatheter brachytherapy can be considered as a valid alternative treatment option after breast conserving surgery.” It could be offered to all women with early-stage, low-risk breast cancer patients in routine clinical practice, he observed.
More evidence is needed before APBI can be considered a new standard, said U.K. commentators in an editorial to accompany the published findings (Lancet. 2015 Oct 19. doi: 10.1016/S0140-6736[15]00471-7).
“This trial presents maturing data and further evidence is required from the 14,000 patients in five, as yet unreported, APBI phase III trials,” saidDr. Charlotte Coles of Cambridge (England) University NHS Foundation Trust and Dr. John Yarnold of the Royal Marsden Hospital NHS Foundation Trust in London in the editorial (Lancet. 2015 Oct 19. doi: 10.1016/S0140-6736[15]00518-8).
Continued follow-up for at least 10 years is planned, “which is essential in view of the linear rate of recurrence for lower risk patients and the ongoing effect of radiotherapy after 5 years of treatment,” Dr. Coles and Dr. Yarnold add.
One of the main reasons for APBI is to reduce the number and duration of treatment from weeks to days and thereby radiation exposure that may result in toxicity. The editorialists noted, however, that recent studies have shown it is possible to give WBI over 3 rather than 5 weeks, and the FAST-Forward trial in the United Kingdom, is looking to see if 1 week is possible.
In the current trial, APBI was delivered at a total dose of 30-32 Gy given in seven to eight fractions over 4-5 days to 633 women, and WBI was given at a total dose of 50 Gy in 25-28 fractions over a 5-week period with a 10 Gy boost to the tumor bed given in five fractions to 551 women.
The median age of the women in the trial was 62 years and 39% had stage I and 51% had stage II cancer. The remainder had stage III or unknown stage disease. The majority of patients had invasive carcinoma (95%), and in 86%, the primary tumor was 2 cm or smaller in size.
“The efficacy of partial breast irradiation is the same as whole breast radiation but is more gentle,” Dr. Strnad observed in an interview.
There fewer grade 2-3 adverse events involving the skin (3.2% vs. 5.7%; P = .08) at 5 years’ follow-up with APBI than with WBI. There was no significant difference between the two radiation modalities in grade 2-3 adverse effects involving the subcutaneous tissue (7.6% vs. 6.3%; P = .053) or grade 3 fibrosis (0% vs. 0.2%; P = .46). No grade 4 late side effects were reported.
“I think the take-home message is that we have two alternatives for radiation therapy after breast-conserving surgery,” Dr. Strnad said. “Everybody should know these data and decide on the most appropriate therapy.”