Partial Breast Irradiation for High Molecular Risk Early-Stage Breast Cancer.

Area of Science:

• Oncology
• Radiation Oncology
• Genomics

Background:

• Partial breast irradiation (PBI) is a recognized alternative to whole breast irradiation (WBI) for early-stage breast cancer.
• Molecular risk scores, like the Oncotype DX recurrence score (ODX RS), are increasingly used for systemic treatment decisions.
• The role of genomic profiling in guiding radiation therapy (RT) decisions, particularly for PBI use in high-risk patients, requires further investigation.

Purpose of the Study:

• To compare oncologic outcomes, specifically local recurrence (LR), between PBI and WBI in patients with a high ODX RS (>25).
• To determine if a high ODX RS should influence the choice between PBI and WBI for breast cancer treatment.

Main Methods:

• A prospectively maintained institutional database was used to identify patients with ODX RS > 25 treated with PBI or WBI after breast conservation.
• Propensity score matching was employed to create comparable PBI and WBI cohorts based on clinicopathologic features (1:5 ratio).
• The primary endpoint evaluated was the incidence of local recurrence (LR) in relation to the radiation therapy approach.

Main Results:

• The study included 968 patients with ODX RS > 25; the matched cohort comprised 28 PBI patients and 140 WBI patients, with a median follow-up of 5.3 years.
• Three LR events occurred in the PBI group (two in different quadrants) and five LR events in the WBI group.
• The 72-month cumulative incidence of LR was 7.9% for PBI versus 4.8% for WBI (P = .6), indicating no statistically significant difference.

Conclusions:

• In patients with a high ODX RS, local recurrence rates were low, with no significant difference observed between PBI and WBI.
• These findings suggest that PBI may be a viable option for carefully selected high-genomic-risk breast cancer patients.
• Larger studies with longer follow-up are necessary to confirm the safety and efficacy of PBI in this population.