Radiotherapy improves outcomes in hormone receptor-positive breast cancer

Women with hormone receptor-positive, low-risk breast cancer achieved significantly higher DFS rates with whole-breast irradiation as part of their postsurgical regimen, according to results from an Austrian trial with 10 years of follow-up presented at European Society for Radiotherapy and Oncology Congress.

The women, who underwent breast-conserving surgery followed by antihormonal treatment, also demonstrated better local control with vs. without whole-breast irradiation.

“Our findings show that radiotherapy is still highly effective in significantly improving local control and DFS in combination with antihormones, compared with antihormones alone. This remains true after long-term follow-up of [patients with] breast cancer with a good prognosis,” Gerd Fastner, MD, associate professor at the clinic of radiotherapy and radio-oncology at University Hospital of Paraclesus Medical University in Salzburg, Austria, said in a press release. “In our analysis, the omission of whole-breast irradiation turned out to be the main predictor for in-breast recurrences. In addition, tumors that could not have their grade classified had a nearly fourfold risk of recurring, which might be due to some of the tumors being more aggressive.”

The 8 A trial of the Austrian Breast and Colorectal Cancer Study Group (ABCSG) included 869 postmenopausal women with low-risk, hormone receptor-positive breast cancer, characterized by grading of G1 or G2, tumor sizes less than 3 cm and node-negative statues. The participants — recruited between 1996 and 2004 — did not receive prior chemotherapy, radiotherapy or hormone therapy.

All women underwent breast-conserving surgery, followed by antihormonal treatment. Researchers then randomly assigned them to receive either whole-breast irradiation (n = 439) or observation (n = 430).

Investigators administered whole-breast irradiation at mean dosages of up to 50 Gy in conventional fractionation. Additionally, 71% received a tumor bed boost at a 10-Gy mean dose.

Median follow-up was 9.89 years.

Ten in-breast recurrences occurred among the whole-breast irradiation group vs. 31 in-breast recurrences in the antihormone treatment-only group, equating to 10-year local control rates of 97.5% vs. 92.4 % (P < .01) and DFS rates of 94.5% vs. 88.4% (P = .01).
Researchers observed a significant DFS advantage after whole-breast irradiation among women who had only sentinel nodes removed (n = 258; HR = 0.25; P = .007), but not among those who underwent axillary dissection (n = 590; HR = 0.7).

At 10 years, the whole-breast irradiation and antihormonal treatment-only groups demonstrated similar rates of metastasis-free survival (96.7% vs. 96.4%) and OS (86.6% vs. 87.6%).

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Multiple Cox regression analysis revealed significant predictors of in-breast recurrence included whole-breast irradiation (HR: 0.27; P < .01) and unknown tumor grading (HR: 3.76; P = .03).

A subsequent analysis of 519 women with accessible gene expression information showed those with levels of Ki67 above 20% or who were HER2-positive did not appear at greater risk for in-breast recurrence.

“We believe that additional benefits of postoperative radiotherapy have been confirmed in hormone receptor-positive patients, regardless of whether they are at high risk [for] breast cancer recurrence,” Fastner said. “In the light of current knowledge, this does not necessarily mean they have to have whole-breast irradiation nowadays, [because] partial-breast irradiation has proved to be competitive. Partial-breast irradiation can be carried out with postoperative hypofractionated external beam radiotherapy, intraoperative techniques or perioperative brachytherapy. The total omission of radiotherapy should only be considered in frail, elderly patients who would not be able to tolerate such treatment.” – by Jennifer Byrne

Reference:

Fastner G, et al. Abstract OC-0270. Presented at: European Society for Radiotherapy and Oncology Congress; April 26-30, 2019; Milan.

Disclosures: HemOnc Today could not confirm the authors’ relevant financial disclosures at the time of reporting.