Partial Breast Irradiation May be as Effective as Whole Breast Irradiation in Preventing Recurrence in Patients with Early Breast Cancer

10-year follow-up data supports earlier findings on recurrence and survival

SAN ANTONIO — A 10-year follow-up study of breast cancer patients who had been treated with accelerated partial breast irradiation (APBI) after surgery showed that their rates of recurrence were similar to those of patients who had received whole breast irradiation (WBI), according to data presented at the 2019 San Antonio Breast Cancer Symposium (SABCS), held Dec. 10–14. The study suggests 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 surgery known as a 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 Italy.

In recent years, researchers have sought to determine whether APBI might be as effective as WBI in preventing recurrence. Meattini’s study examined 10-year follow-up data for women enrolled in the APBI IMRT trial, a randomized phase III trial. The five-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 1 or stage 2 breast cancer. Between 2005 and 2013, the patients were randomly assigned in a 1:1 ratio to receive either APBI or WBI. The patients in the APBI arm received a total of 30 Gray (Gy) of radiation to the tumor bed in five daily fractions, while 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.

The study showed that after 10 years, 3.3 percent of patients in the APBI group had experienced a recurrence of breast cancer, compared to 2.6 percent in the group that received WBI. These

results were comparable to the five-year results, in which the group that received APBI had a 2.4 percent recurrence rate, and the group that received WBI had a 1.2 percent recurrence rate. Both differences were not statistically significant.

Overall survival at the 10-year mark was also very similar between the two groups: 92.7 percent for the women who had received APBI and 93.3 percent for the women who received WBI.

Breast-cancer specific survival was 97.6 percent for those who received APBI and 97.5 percent for those who received WBI.

The distant metastasis-free survival rate was 96.9 percent both for the women who received APBI and for those who received WBI.

“These results reinforce the initial promising results from the previous study,” Meattini said. “Accelerated partial breast irradiation can produce excellent disease control.”

Partial breast vs. whole breast radiation has been a topic of multiple clinical trials. A study presented at SABCS in 2018 showed that while the results were close, WBI proved slightly more effective in reducing recurrence rates.

Meattini said this growing body of research may help clinicians recommend that patients at lower risk of recurrence choose to receive APBI, while those at a higher risk of recurrence may be recommended for WBI.

“In well-selected cases, there is no difference in patients’ outcomes whether they are treated with APBI or WBI,” he said. “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.” He 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 de-escalation of treatment in breast oncology,” Meattini said. “For many patients, partial breast irradiation may be an optimal choice that is cost-effective, safe, and efficacious.”

Meattini said the study’s chief limitation is its relatively small size. 

This study was supported by the Radiation Oncology Unit of the Florence University Hospital. Meattini declares no conflicts of interest.