Can very low-risk breast cancer patients be spared from postop radiotherapy?

Adjuvant radiotherapy (RT) may be omitted in women with very low-risk breast cancer who have had breast conserving surgery (BCS) and have been receiving endocrine therapy, according to findings from the LUMINA study.

Adjuvant RT is typically prescribed post-BCS to reduce risk of local recurrence, noted Dr Timothy Joseph Whelan from McMaster University, Hamilton, Ontario, Canada, at ASCO 2022. “However, it is inconvenient for the patient, often requiring daily treatments for up to 5 weeks.”

“[Moreover, it] is costly and is associated with significant toxicity – both acute (eg, skin erythema, irritation, fatigue) and late (eg, breast pain, induration, breast distortion), which can affect cosmesis and quality of life. It is also associated with rare life-threatening side effects (eg, cardiac disease, second cancers),” Whelan continued.

Due to improvements in surgical techniques, effective adjuvant systemic therapy, and smaller screen-detected cancers, the last 2 decades have seen a reduction in the rates of local recurrence.

As such, Whelan raised an important question: Can RT be omitted in very low-risk patients?

“[Our study showed that] women with low-risk clinical pathologic factors and luminal A* breast cancer following BCS receiving endocrine therapy alone for 5 years had a very low rate of local recurrence,” he said.

Only 10 local recurrences – all invasive – were identified. Local recurrence was defined as any invasive or noninvasive cancer in the ipsilateral breast. Looking at the cumulative incidence curve, the rate gradually rose to 2.3 percent over 5 years. [ASCO 2022, abstract LBA501]

“This rate satisfied our prespecified boundary [of <5 percent, and] was an acceptable low risk,” Whelan continued. “[Hence, our findings suggest] that such patients are candidates for omission of RT.”

Regarding secondary outcomes, there were eight contralateral breast cancer events, yielding a 5-year cumulative rate of about 2 percent. According to Whelan, this is quite comparable to the risk of local recurrence in the treated breast.

For any recurrence, there were 12 events identified (5-year rate, 2.7 percent). For disease-free survival, there were 47 events, half of which were second primary non-breast cancers (5-year rate, 89.9 percent). Of the 13 overall survival events, one was death due to breast cancer.

The analysis included 500 women (mean age 67 years, mean tumour size 1.1 cm) who have undergone BCS for T₁N₀ grade 1–2 (66 percent grade 1) breast cancer luminal A subtype who have been on adjuvant endocrine therapy. Of these, four received RT, eight did not receive endocrine therapy, while 21 withdrew from follow-up, which was conducted every 6 months for the first 2 years and annually thereafter. About 60 percent were treated with aromatase inhibitor while the rest received tamoxifen.

“Over 300,000 women are diagnosed yearly with invasive breast cancer in North America. We estimate that our results could apply to [up to] 40,000 women per year who could avoid the morbidity, inconvenience, and cost of RT,” Whelan concluded.