RT may be omitted after breast-conserving surgery in T1N0, grade 1/2, luminal A breast cancer

Radiotherapy (RT) may be omitted in women ≥55 years of age with T1N0, grade 1 or 2, luminal A breast cancer who have been treated with breast-conserving surgery and endocrine therapy, due to the very low risk of 5-year local recurrence reported in a recent prospective cohort study.

The study included 500 patients (median age, 67.1 years; median tumour size, 1 cm) recruited across 26 centres in Canada. The patients had undergone breast-conserving surgery for T1N0, grade 1 or 2, lumina A subtype breast cancer (defined as oestrogen receptor positivity ≥1 percent, progesterone receptor positivity >20 percent, negative HER2, and Ki67 index ≤13.25 percent), and had received adjuvant endocrine therapy (aromatase inhibitor, 59 percent; tamoxifen, 41 percent). These patients did not receive RT. They were followed prospectively, every 6 months for 2 years and subsequently annually, for recurrent invasive or in situ cancer of the ipsilateral breast as the primary outcome. [N Engl J Med 2023;389:612-619]

“In consultation with radiation oncologists and patients with breast cancer, we determined that if the upper boundary of the two-sided 90 percent confidence interval [CI] for the cumulative incidence of local recurrence at 5 years was less than 5 percent, this would represent an acceptable risk,” the researchers noted.

At 5 years after enrollment, the cumulative incidence of local recurrence was 2.3 percent (90 percent CI, 1.3–3.8; 95 percent CI, 1.2–4.1), which met the presepcified boundary. Among 10 of the 500 patients with local recurrence, all were invasive, with six deemed to be true or marginal recurrences and four occurring elsewhere in the ipsilateral breast.

Contralateral breast cancer occurred in 1.9 percent of the patients (90 percent CI, 1.1–3.2), all of which were invasive. Recurrence of any type occurred in 2.7 percent of the patients (95 percent CI, 1.6–4.1), including two distant recurrences, no regional recurrence, and 10 local recurrences.

The 5-year disease-free survival rate was 89.9 percent, while 5-year overall survival rate was 97.2 percent.

“The use of intrinsic subtyping in combination with clinicopathologic risk factors to identify [low-risk] patients in whom RT could be omitted would be a major change in practice,” the researchers noted.

“The incidence of recurrence in the ipsilateral breast was similar to that of new breast cancers observed in the contralateral breast – findings that confirmed the low risk and suggested that at least some of the ipsilateral breast cancers may have been new breast cancers,” they suggested. “The risks of distant recurrence and death due to breast cancer were also very low.”

“The very low risk of local recurrence at 5 years after breast-conserving surgery observed in our prospective cohort study supports our conclusion that women ≥55 years of age with T1N0, grade 1 or 2, luminal A breast cancer treated with endocrine therapy after breast-conserving surgery are candidates for omission of RT,” they noted.