Accelerated Partial Breast Irradiation Could Replace Whole Breast Irradiation in Low-Risk Early Breast Cancer

Icro Meattini, MD

Accelerated partial breast irradiation (APBI) using intensity-modulated radiotherapy is not significantly different from whole breast irradiation (WBI) in preventing recurrence in patients with low-risk early breast cancer, according to 10-year follow-up data from the APBI IMRT Florence (NCT02104895) trial presented at the 2019 San Antonio Breast Cancer Symposium (SABCS).¹

At 10 years, 3.9% of patients who received APBI had experienced ipsilateral breast cancer recurrence compared with 2.6% in those who received WBI (HR, 1.57; 95% CI, 0.56-4.41; P = .39), which was not determined to be statistically significant. Very low rates of events were observed, according to Meattini, with 9 events observed in the APBI arm versus 6 events in the WBI arm.

“Recent developments in radiation oncology for breast cancer show a faster move toward de-escalation strategies, including APBI,” said lead study author, Icro Meattini, MD, of the University of Florence in Italy. “What we’ve learned from major phase III trials…is that [with partial breast radiation,] disease control is closely related to the adequate selection of patients. The safety profile and cosmetic outcome is more strongly associated with the technique.”

Furthermore, no significant difference in the locoregional recurrence rates were observed between the 2 arms; 3.9% and 3.0% of patients experienced locoregional recurrence in the ABPI and WBI arms, respectively, with 9 events versus 7 events reported, respectively.

“Postoperative radiation still represents a mainstay of adjuvant treatment for breast cancer, and is able to significantly reduce the local relapse occurrence rate,” said Meattini in a press release.² However, it has been largely unknown whether APBI to the tumor-bearing quadrant, which shortens treatment duration, is equally effective to that of standard WBI.

To this end, the phase III APBI IMRT Florence equivalence trial was launched. A total of 520 patients over the age of 40 with either stage 1 or stage 2 breast cancer were enrolled. These patients received breast-conserving surgery, had a pT of <25 mm, and final surgical margins ≥5 mm.

Between 2005 and 2013, participants were randomized 1:1 to receive either APBI or WBI. Patients in the ABPI arm were given a total of 30 Gy of radiation to the tumor bed in 5 fractions, non-consecutively; those on WBI received 50 Gy of radiation to the whole breast in 25 fractions, plus 10 Gy to the tumor bed in 5 fractions.

Five-year survival data from the trial were presented at the 2014 SABCS.³ At a median follow-up of 5 years (interquartile range, 3.4-7.0), the rate of recurrence was 1.5% in both the APBI (95% CI, 0.1-3.0) and WBI (95% CI, 0.0-2.8) arms. No statistically significant difference emerged between the 2 arms (log rank test P = .86). The 5-year overall survival (OS) rates were 96.6% and 99.4% in the WBI and APBI arms, respectively, which was not statistically significant.

At 10 years, OS was still found to be similar between the 2 groups: 92.7% in the APBI group versus 93.3% in the WBI group (HR, 0.99; 95% CI, 0.49-2.00; P = .097). In terms of breast cancer-specific survival, investigators reported a rate of 97.6% in the APBI arm compared with 97.5% in the WBI arm, with 5 and 6 events reported, respectively (HR, 0.87; 95% CI, 0.26-2.86; P = .82). With regard to distant metastases, 7 events were reported in each arm, translating to a distant metastasis-free rate of 3.1% in both groups of patients (HR, 1.03; 95% CI, 0.36-2.94; P = .95).

“These results reinforce the initial promising results from the previous study,” Meattini said in the press release. “APBI can produce excellent disease control.”

Acute adverse events (AEs) were assessed based on the RTOG and EORTC acute toxicity scale. Results showed that 78.9% of patients in the APBI arm did not experience any skin toxicity compared with 33.5% of those on WBI.

Seventeen grade 3 events (6.5%) were reported in the WBI arm, whereas no events grade ≥2 were reported in the APBI arm. A total of 47 and 75 grade 1 AEs were reported in the APBI and WBI arms, respectively; 5 grade 2 events were observed with APBI versus 81 events with WBI.

Data regarding late AEs were also in favor of APBI (n = 11) versus the WBI arm (n = 78).

Investigators used the Harvard Breast Cosmesis Scale to evaluate the effect of radiation therapy on cosmesis. An excellent cosmetic result was reported by physicians in 95.5% of patients in the APBI group versus 76.5% of those in the WBI group (P = .0001). More excellent cosmetic results were also reported by patients on APBI compared with on WBI (17.9% vs 5.4%).

These data add to the growing body of research exploring APBI in comparison with WBI, which have been mixed. At the 2018 SABCS, data from the phase III NSABP B-39/RTOG 0413 trial showed that APBI following lumpectomy was not found to be equivalent to WBI to control recurrence, although the differences relative to both strategies were very small.⁴

“This is just another piece of the puzzle; [based on these data,] APBI might be considered a standard alternative to WBI in patients with low-risk early breast cancer,” said Meattini in a press conference during the meeting. He added that patients who are at a higher risk of recurrence may benefit more from WBI.

“In well-selected cases, there is no difference in patients’ outcomes whether they are treated with APBI or WBI,” he concluded. “A once-daily regimen of external APBI might also produce an improved quality of life, with less toxicity, and can potentially reduce the overall treatment time.”

References

1. Meattini I, Saieva C, Lucidi S, et al. Accelerated partial breast or whole breast irradiation after breast conservation surgery for patients with early breast cancer: 10-year follow up results of the APBI IMRT Florence randomized phase 3 trial. Presented at: 2019 San Antonio Breast Cancer Symposium; December 10-14, 2019; San Antonio, TX. Abstract GS4-06. bit.ly/34dV67F.
2. Partial breast irradiation may be as effective as whole breast irradiation in preventing recurrence in patients with early breast cancer [news release]. San Antonio, TX: American Association for Cancer Research; December 12, 2019. bit.ly/2PDhbY6. Accessed December 12, 2019.
3. Livi L, Meattini I, Marrazzo L, et al. Accelerated partial breast irradiation using intensity-modulated radiotherapy versus whole breast irradiation: 5-year survival analysis of a phase 3 randomised controlled trial. Eur J Cancer. 2015;51(4):451-463. doi: 10.1016/j.ejca.2014.12.013.
4. Vicini F, Cecchini R, White J, et al. Primary results of NSABP B-39/ RTOG 0413 (NRG Oncology): A randomized phase III study of conventional whole breast irradiation (WBI) versus partial breast irradiation (PBI) for women with stage 0, I, or II breast cancer. Presented at: 2018 San Antonio Breast Cancer Symposium; December 4-8, 2018; San Antonio, TX. Abstract GS4-04.

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