Older women with early-stage breast cancer may not need radiotherapy after undergoing surgery, McMaster researcher Timothy Whelan and his team have found.

Women 55 or older with Stage 1 breast cancer displaying a specific biomarker pattern identifying the luminal A subtype can be effectively treated with just surgery and endocrine therapy, Whelan said.

Whelan, a professor in the department of oncology and the Canada Research Chair in Breast Cancer Research, presented his findings at the American Society of Clinical Oncology’s annual meeting in Chicago on June 7.

Whelan’s research team, working with the Ontario Clinical Oncology Group at Hamilton Health Sciences (HHS), tracked 501 patients with luminal A breast cancer for five years post-surgery and found the recurrence of cancer in the breast was just 2.3 per cent without radiotherapy. This was roughly comparable with a 1.9-per-cent risk this patient sample had of developing a new breast cancer in the other, untreated breast.

At this time, patients with early stage breast cancer typically undergo radiotherapy courses of three to five weeks to reduce the risk of their cancer recurring, said Whelan, who is a radiation oncologist for HHS.

“These findings are exciting because we have identified a certain group of patients who can avoid radiotherapy and its associated side effects and potentially change for the better medical practice around the treatment of breast cancer,” said Whelan

“Radiotherapy has significant early side effects, including fatigue and skin irritation that can last for several weeks after the course is completed, and late side effects such as breast shrinkage and distortion that can affect quality of life and very rarely more serious complications such as heart disease and second cancers,” he said.

“If we can avoid radiotherapy, so much the better. Not all cancers require the same level of often invasive treatment. There is a very low risk group of breast cancers displaying the luminal A biomarker and they are not particularly aggressive.”

The overall risk of cancer recurrence following breast-conserving surgery has decreased in recent years because of regular mammogram screening, improved surgical techniques and better systemic treatments, Whelan said.

His research is now tracking patients with the luminal A variant of breast cancer for 10 years to learn more about treatment efficacy without the use of radiotherapy.