CHICAGO Women with breast cancer who want to take advantage of the more convenient course of partial breast irradiation (PBI) can now rest assured they are not going to have worse cosmetic outcomes by foregoing whole breast irradiation (WBI). This is the conclusion from the final report from the pivotal phase 3 trial (RTOG 0413) that compared the two approaches.

"I think this trial has confirmed the ASTRO consensus statement" that describes the patient population that is suitable for PBI, commented lead author Julia White, MD, professor of radiation oncology at the Ohio State University Comprehensive Cancer Center.

"A good population for PBI includes women over the age of 50 who have stage 1 breast cancer that is hormone sensitive, who take endocrine therapy for it, as well as ductal carcinoma in situ (DCIS) patients whose tumors are less than 2.5 cm in size," she said.

"These patients, who represent probably around 30,000 women a year, need to know that PBI is a good alternative for their cancer outcome and now, I don't think concern about cosmetic outcomes should be a barrier," she added.

White was speaking here at a press briefing at the American Society for Radiation Oncology (ASTRO) annual meeting, where she presented the final report from this trial.

The NRG Oncology/NSABP B39-RTOG 0413 study involved more than 4000 women with stage 0, I, or II breast cancer who had undergone a lumpectomy and were randomly assigned to either WBI or PBI.

WBI was administered at a dose of 50 Gy at 2.0 Gy/fraction or 50.4 Gy at 1.8 Gy/fraction to the whole breast, followed by an optional boost to 60 Gy for 5 to 6 weeks.

Women assigned to the PBI arm received 10 fractions, twice a day, for 5 to 8 days at a dose of 34 Gy in 3.4 Gy fractions. PBI was delivered via interstitial brachytherapy or by mammosite balloon catheter or in a dose of 38.5 Gy in 3.85 Gy delivered in 3-dimensional conformal radiotherapy.

Previously reported oncological outcomes from this trial showed that breast recurrence rates after PBI were within 1% of breast recurrence rates after WBI.

"The really good news was that 95% of all women had no recurrence out to 10 years," White added, "and the risk for distant metastases after each procedure was also pretty close at between 1% to 2% between the two approaches," she said.

At the ASTRO meeting, White presented results from a quality of life substudy that showed that cosmetic outcomes were equivalent between WBI and PBI as well.

In the substudy involving 900 women, breast cosmesis was assessed by the patients themselves, as well as by the accruing-site physician and by central review of digital photos by physicians blinded to the randomized treatment arm. Digital photos of the breasts were collected at baseline, and at 1 and 3 years after patients received either WBI or PBI.

The goal of the current substudy was to see if PBI induced changes in breast appearance that were equivalent to those induced by WBI as assessed by the 3 separate groups using the Global Cosmetic Score (GCS).

"Patients were stratified by chemotherapy use and no-chemotherapy use," the investigators noted. Just under half (47%) of the group had received chemotherapy.

Based on the patients' own assessment, changes in cosmetic outcomes at 36 months were equivalent for women who received WBI or PBI based on GCS scores in both chemotherapy recipients and nonchemotherapy recipients at 0.06 vs 0.04, respectively.

When the two groups were combined, change in cosmetic outcomes at 36 months were again equivalent at a GCS of 0.045, as White reported.

Judged by accruing-site physicians, change in the GCS again at 36 months was not quite equivalent in chemotherapy receipts who received PBI compared with WBI, and the same was true in nonchemotherapy recipients. In both groups, cosmetic outcomes were judged to be slightly worse following PBI compared with WBI, White reported.

However, when the two groups were combined, GCS changes were equivalent between PBI and WBI at a change in GCS score of 0.045, she observed.

When the digital photos were assessed by central reviewers, cosmetic outcomes were not equivalent among chemotherapy users, where PBI was deemed to be inferior to WBI.

However, the reverse was true for patients who did not undergo chemotherapy, among whom cosmetic outcomes in breasts treated with WBI were judged to be worse than they were for breasts treated with PBI.

Again, however, when the two groups were combined, cosmetic outcomes as assessed by central reviewers were felt to be equivalent for PBI and WBI, at a change in GCS of 0.028.

White also noted that there were no significant differences in mean changes in GCS as assessed by both patients and by digital photos reviewers at each time point that cosmesis was assessed during the study interval.

The only differences observed between mean changes in GCS at each time point of assessment were seen among accruing-site physicians who, at 36 months, rated changes in cosmetic outcomes at 0.43 for breasts treated with PBI vs 0.17 for breasts treated with WBI, which was statistically significant (P = .001).

On the other hand, patient satisfaction with cosmetic outcomes in those who had received chemotherapy, those who had not received chemotherapy, and the combination of the two groups were all equivalent between those who had undergone WBI and those who had received PBI.

"I think this is the link we were waiting for," White observed.

White noted that an earlier, similarly designed study referred to as the RAPID trial again demonstrated that the accelerated PBI regimen used in the trial was noninferior to WBI in preventing local recurrence, but there was an increase in late normal tissue toxicity and cosmetic outcomes were judged to be worse with PBI than with WBI.

"Thus, there was concern that women would have to sacrifice the appearance of their breast to undergo more convenient radiation," White said.

"But from our analysis, we feel pretty confident that from a patient perspective, there was no difference between treatment arms, and that one arm did not cause more change [in cosmetic outcomes] than the other," she concluded.

Commenting on the findings, Wendy Woodward, MD, professor of radiation oncology, MD Anderson Cancer Center in Houston, Texas, told the press briefing that the outstanding question at the time the RTOG 0413 trial was designed was whether there would be a similar detriment in cosmetic outcomes following PBI as was shown in the RAPID trial.

"Looking at the data very granularly, it is patient satisfaction and patient-reported outcomes that really matter and in this trial, [and these assessments] were completely equivalent," Woodward said.

"So I think this study is a cornerstone for highlighting that PBI is now standard of care for eligible patients and, ultimately, we will see these papers published and we will see practice change as PBI becomes a standard-of-care option," she concluded.

White disclosed travel expenses from IBA and Qfix. Woodward declared she has served as a consultant for Global Health International.

American Society for Radiation Oncology (ASTRO) 2019 Annual Meeting: Abstract #5. Presented September 16, 2019.

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Cosmetic Outcomes Equal After Partial vs Whole Breast Radiation - Medscape

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