A new study suggests that oncologists can safely pull back on standard locoregional radiotherapy (RT) in select patients with cT1-2N1 breast cancer who are treated with primary chemotherapy prior to surgery. The key is to divide patients by risk level and treat them according to the study’s guidelines, the researchers reported.
lead study author Sabine de Wild, MD, a PhD student at Maastricht (the Netherlands) University Medical Center, said in an interview.
The study, published in The Lancet Oncology, was intended to provide insight into which breast cancer patients need adjuvant locoregional radiotherapy following postchemotherapy surgery, coauthor Liesbeth Boersma, MD, PhD, a radiation oncologist at Maastricht University Medical Center, said in an interview. “It is not yet known which of these patients would benefit from adjuvant locoregional radiotherapy and to what extent the response of the tumor to the chemotherapy should be taken into account.”
For the study, believed to be the first prospective analysis tackling this topic, researchers tracked 838 patients in The Netherlands who were treated for cT1-2N1 breast cancer with primary chemotherapy and surgery of the breast and axilla from 2011-2015. Tumors were less than 5 cm and metastases were one to three axillary nodes.
The subjects were divided into groups based on risk of locoregional recurrence, and each group underwent different therapies.
- Low-risk group: no metastases were present in the nodes (n = 291). “We omitted regional radiotherapy, and we omitted RT of the chest wall in case of a mastectomy. After breast conserving surgery, regular RT of the breast was recommended,” Dr. de Wild said.
- Intermediate-risk group, one to three metastases were still present (n = 370). “We omitted regional radiotherapy, but irradiated the chest wall or breast,” she said.
- High-risk group, three metastases were present (n = 177). “We did not de-escalate, and all patients were treated with locoregional RT,” she said.
According to the study, “the 5-year locoregional recurrence rate in all patients was 2.2% (95% confidence interval, 1.4-3.4). The 5-year locoregional recurrence rate was 2.1% (95% CI, 0.9-4.3) in the low-risk group, 2.2% (95% CI, 1.0-4.1) in the intermediate-risk group, and 2.3% (95% CI, 0.8-5.5) in the high-risk group.”
In 26% of cases, patients received more radiotherapy than the study guidelines suggested. “Remarkably,” the researchers wrote, “this did not seem to affect locoregional recurrence rate, recurrence-free interval, and overall survival in a statistically significant or clinically relevant way.”
As for limitations, the authors noted that, “in each risk group, the actual sample size treated according to the study guideline was smaller than required based on the power calculation. Nevertheless, when performing the analyses in the subset of patients treated according to the study guideline, the upper limit of 95% CI of 5-year locoregional recurrence rate did not exceed 7.8%.”
The study authors wrote that, “in the future, the results of this study might lead to more frequent omission of locoregional radiotherapy, which could result in lower morbidity and a better quality of life for patients with breast cancer who are receiving primary chemotherapy.”
However, Dr. de Wild said randomized trials are necessary “to investigate how treatment can be individualized further, i.e., by taking into account specific tumor characteristics.” Also, most patients in the study underwent axillary lymph node dissection, “while patients in daily practice may instead undergo targeted axillary dissection. Future studies are needed to determine if less radiotherapy is also safe in patients in whom axillary lymph node dissection is omitted.”
The study was funded by the Dutch Cancer Society. One coauthor reported a pending patent plus grants from AstraZeneca, Eurocept Plaza, Roche, Genentech, Gilead Sciences, Tesaro, Novartis, Dutch Cancer Society, ZonMw, and A Sister’s Hope; as well as consulting fees and other financial support from a variety of pharmaceutical companies. The other authors had no disclosures.
