Women with early breast cancer had similar long-term outcomes whether they had focused or whole-breast irradiation (WBI), an Italian study showed.
The 10-year incidence of in-breast tumor recurrence (IBTR) was 2.5% with WBI and 3.7% with accelerated partial breast irradiation (APBI), a difference that did not reach statistical significance. Patients in both arms had a 10-year overall survival (OS) of 91.9% and breast cancer-specific survival (BCSS) of 97%-98%. The data showed a trend favoring APBI for a reduced risk of contralateral breast cancer recurrence, according to Icro Meattini, MD, of the University of Florence, and colleagues.
APBI was associated with significantly less toxicity, and physicians and patients considered the cosmetic outcomes better with APBI, they reported in the Journal of Clinical Oncology.
“The long-term update of our trial confirmed the previously published promising findings at a 5-year median follow-up,” Meattini concluded. “We observed few IBTR events at a median follow-up of 10 years and an absolute cumulative difference of 1.2% at 10 years, nonsignificantly in favor of the WBI arm.
“Depending on the value placed on IBTR, this absolute IBTR difference between arms might be considered as not clinically relevant. Indeed, distant control of disease as well as BCSS and OS were comparable between arms.”
The long-term follow-up results from the Florence trial supported data from previous trials demonstrating similar outcomes with APBI. The only phase III trial that did not meet its endpoint tested for the equivalence of the two radiation therapy techniques, not noninferiority. That study showed only a 0.7% difference in 10-year local recurrence and no differences in survival outcomes, said Frank Vicini, MD, of 21st Century Oncology in Farmington Hills, Michigan.
“There are now six other prospective randomized trials (including Florence) with more than 6,000 women followed from 5-10 years, and none of the other studies show a statistically significant difference in outcome,” said Vicini, principal investigator in the equivalence trial and an expert source for the American Society for Radiation Oncology. “There are guidelines for the optimal application of APBI (who qualifies) and if a patient does, the data support APBI as an acceptable and equivalent option and the Florence trial convincingly demonstrates and reinforces that.”
“The Florence trial is important because it is now the third phase III trial with at least 10 years of follow-up that demonstrates no difference in outcome (local recurrence or survival),” he told MedPage Today by email. “In other words, it is important to demonstrate that the excellent 5-year results seen with APBI in the current study (and the six other phase III trials using APBI) are stable on long-term follow-up reinforcing it as an equivalent option for many women undergoing treatment for early-stage breast cancer. The long-term results are also important because they demonstrate the stability of the excellent cosmetic results achieved with APBI.”
The Florence trial included 520 patients older than age 40 with early breast cancer suitable for treatment with breast conservation. They were randomized to WBI (50 Gy in 25 fractions, plus 10-Gy boost to the surgical bed) or to APBI (intensity modulated RT, 30 Gy in five nonconsecutive once-daily fractions, equivalent to 54 Gy in 2-Gy fractions). The primary endpoint equivalent 5-year IBTR, defined as local recurrence and new ipsilateral breast tumors. Equivalence was defined as no more than a 5% absolute difference in IBTR.
As the authors noted, the trial met the primary endpoint. Follow-up continued to assess the long-term stability of the results.
After a median follow-up of 10.7 years, the 1.2% absolute difference in IBTR represented a hazard ratio of 1.56 in favor of WBI but did not achieve statistical significance or fall outside the 5% boundary for equivalence (95% CI 0.55-4.37). Other 10-year outcomes also did not differ significantly between the two groups, including:
- Locoregional recurrence: 2.9% with WBI vs 3.7% with APBI (HR 1.33, 95% CI 0.49-3.56, P=0.58)
- Contralateral breast cancer: 3.2% vs 0.8% (HR 0.25, 95% CI 0.05-1.18, P=0.08)
- BCSS: 96.7% vs 97.8% (HR 0.65, 95% CI 0.21-1.99, P=0.45)
- OS: 91.9% in each arm
APBI was associated with significantly less acute and late toxicity (P=0.0001 for each comparison). Physicians and patients rated long-term cosmetic outcomes superior with APBI (P=0.0001 for both).
Multiple biology-driven clinical trials are ongoing in an effort to identify the best candidates for APBI, the authors noted.
The study was sponsored by Azienda Ospedaliero-Universitaria Careggi.
One or more authors disclosed relevant relationships with Elekta, Boehringer Ingelheim, MSD oncology, AstraZeneca/MedImmune, Roche/Genentech, Bristol-Myers Squibb, Pfizer, Merck Serono, and Angelini Pharma.