Omitting RT After Lumpectomy Yields 14.8% 5-Year Local Recurrence in Older Women

Omitting postoperative radiotherapy (RT) after breast-conserving surgery (BCS) in systemically untreated women aged 70 years or older with low-risk, early-stage estrogen receptor (ER)-positive breast cancer resulted in a 5-year invasive local recurrence (LR) risk of 14.8%, according to 5-year results from the prospective TOP-1 study (BOOG 2016-01).

At the 2026 European Society for Medical Oncology (ESMO) Congress, Lotte Bouwman, MD, a PhD candidate in surgical oncology at Leiden University Medical Center in the Netherlands, presented the findings during a rapid oral session on early-stage breast cancer.¹

In a cumulative incidence analysis with death as a competing event, the 5-year LR risk was 14.8% (95% CI, 12.3%-17.4%) among the 792 patients included in the primary analysis. LR, defined as a pathologically confirmed invasive ipsilateral breast tumor, increased gradually over time, with 7 events by year 1, 24 by year 2, 53 by year 3, 85 by year 4, and 111 by year 5. At a median follow-up of 5.1 years (4.9-5.2), a total of 123 LRs had been recorded. Other events during follow-up included regional recurrence in 14 patients (1.8%), distant metastasis in 7 (0.9%), a contralateral new primary breast tumor in 32 (4.0%), and a non-breast new primary tumor in 52 (6.6%). Nine patients had a noninvasive LR, and some patients experienced more than 1 event.

Despite the LR rate, survival outcomes were favorable. The 5-year overall survival (OS) rate was 89.6% (95% CI, 87.4%-91.9%), and the 5-year breast cancer-specific survival (BCSS) rate was 99.7% (95% CI, 99.4%-100%). Of the 81 patients who died during follow-up, 3 deaths (3.7%) were related to breast cancer, and 78 (96.3%) were not related to breast cancer or had an unknown cause. Five patients were lost to follow-up.

Most LRs were salvageable with further local treatment. Among the 123 patients with an LR, 114 (92.7%) underwent surgery, of whom 86 (75.4%) had a repeat BCS and 28 (24.6%) had a mastectomy; 8 patients (6.5%) did not undergo surgery. In addition, 70 patients (56.9%) received RT, 43 (35.0%) received endocrine therapy, 3 (2.4%) received chemotherapy, and 2 (1.6%) received immunotherapy for their recurrence. Treatment was unknown in 1 patient.

TOP-1 was a prospective, multicenter, observational, single-arm study that enrolled women aged 70 years or older with early-stage breast cancer between January 2017 and September 2021. Eligible patients had tumors that were ER positive (at least 50%) and HER2 negative, with T1 disease measuring 1 cm or less and grade 1 or 2, or 2 cm or less and grade 1. Patients were also required to have negative surgical margins and a negative sentinel node. All patients underwent BCS without postoperative treatment, meaning neither RT nor endocrine therapy was administered.

The study aimed to assess the 5-year invasive LR risk after BCS, with overall survival and BCSS as additional aims. According to the presenter, RT is the standard of care after BCS, and its omission is known to increase the 5-year risk of LR. Meanwhile, the Dutch breast cancer guideline recommends against endocrine therapy for clinically low-risk breast cancer, creating a population of patients treated with lumpectomy alone.

The median age of patients at baseline was 73.6 years (IQR, 71.9-75.5). Most patients had pT1b tumors measuring more than 5 mm to 10 mm (55.3%), followed by pT1c tumors measuring more than 10 mm to 20 mm (32.6%) and pT1a tumors measuring 5 mm or less (10.7%). Overall, 83.5% of tumors were progesterone receptor positive, 75.5% were grade 1, and 24.0% were grade 2. Most tumors were of no special type (78.4%), followed by lobular (8.5%), mucinous (5.3%), and tubular (2.8%) histologies; 38.5% of patients had invasive disease with accompanying ductal carcinoma in situ.

The investigators concluded that, although RT remains a cornerstone of breast cancer treatment, its omission may be an option for a subgroup of older patients through shared decision-making, given that repeat BCS was possible in most patients who experienced an LR and survival was excellent. Future research will include longer follow-up, assessment of quality of life, and efforts to predict which patients are at higher risk of LR.

Reference

Bouwman L, Liefers GJ, et al. Omission of postoperative radiotherapy after breast-conserving surgery in systemically untreated older patients with early-stage ER+ breast cancer: 5-year results of the TOP-1 study (BOOG 2016-01). Presented at: 2026 European Society for Medical Oncology Congress; October 23-27, 2026; Madrid, Spain. Abstract 545RO.