A 10-year follow-up study of patients with breast cancer who had been treated with accelerated partial-breast irradiation (APBI) after surgery showed that their rates of disease recurrence were similar to those of patients who had received whole-breast irradiation (WBI), according to data presented by Meattini et al at the 2019 San Antonio Breast Cancer Symposium (Abstract GS4-06). The study results suggest that the less invasive partial-breast procedure may be an acceptable choice for patients with early breast cancer.

Many patients diagnosed with early breast cancer undergo lumpectomy followed by a course of radiation. “Postoperative radiation still represents a mainstay of adjuvant treatment for breast cancer, able to significantly reduce the local relapse occurrence rate,” explained the study’s lead author, Icro Meattini, MD, of the University of Florence, in a statement. In recent years, researchers have sought to determine whether APBI might be as effective as WBI in preventing recurrence.

Study Methods

Dr. Meattini’s study examined 10-year follow-up data for women enrolled in the APBI IMRT trial, a randomized phase III trial. The 5-year follow-up from the trial showed no significant difference in tumor recurrence or survival rates.

The APBI IMRT trial enrolled 520 women over age 40 who had either stage I or II breast cancer. Between 2005 and 2013, the patients were randomly assigned 1:1 to receive either APBI or WBI. The patients in the APBI arm received a total of 30 Gy of radiation to the tumor bed in five daily fractions, whereas those in the WBI arm received a total of 50 Gy in 25 daily fractions to the whole breast, plus a boost of 10 Gy to the tumor bed in five daily fractions.

Both treatment arms were comparable in terms of age, tumor size, tumor type, and adjuvant endocrine treatment, and both achieved a median 10-year follow-up. The majority of the patients had hormone receptor–positive, HER2-negative breast cancer, and most were over age 50.

10-Year Follow-up

The study showed that after 10 years, 3.3% of patients in the APBI group had experienced a recurrence of breast cancer compared to 2.6% in the group that received WBI. These results were comparable to the 5-year results, in which the group that received APBI had a 2.4% recurrence rate, and the group that received WBI had a 1.2% recurrence rate. Neither difference was statistically significant.

Overall survival at the 10-year mark was also very similar between the two groups: 92.7% for the women who had received APBI and 93.3% for the women who received WBI. Breast cancer–specific survival was 97.6% for those who received APBI and 97.5% for those who received WBI. The distant metastasis-free survival rate was 96.9% both for the women who received APBI and for those who received WBI.

“These results reinforce the initial promising results from the previous study,” said Dr. Meattini. “APBI can produce excellent disease control.” He noted that the study’s chief limitation is its relatively small size.

“In well-selected cases, there is no difference in patients’ outcomes whether they are treated with APBI or WBI,” he continued. “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.” Dr. Meattini added that APBI may also be less likely to cause cosmetic changes and is less expensive to administer than WBI.

“Partial-breast irradiation is one of the primary examples of effective deescalation of treatment in breast oncology,” he said. “For many patients, partial-breast irradiation may be an optimal choice that is cost-effective, safe, and efficacious.”

Disclosure: This study was supported by the Radiation Oncology Unit of the Florence University Hospital. For full disclosures of the study authors, visit abstractsonline.com.