# Efficacy of Metastasis-Directed Radiation Therapy to Prolong Systemic Therapy for Patients with Oligoprogressive Metastatic Breast Cancer

## TL;DR

This study found that about 60% of patients with a specific type of advanced breast cancer stayed on the same treatment for at least six months after receiving targeted radiation therapy.

## Contribution

The study provides evidence that metastasis-directed radiation therapy may prolong systemic therapy duration in oligoprogressive metastatic breast cancer patients.

## Key findings

- 60% of patients with oligoprogressive metastatic breast cancer remained on the same systemic therapy for at least 6 months after MDRT.
- Among patients with a follow-up of at least one year, 47% stayed on the same systemic therapy after MDRT.
- The median time to next systemic therapy and progression-free survival were 6.9 and 6.2 months, respectively.

## Abstract

Clinical trials have shown mixed results regarding the benefit of metastasis-directed radiation therapy (MDRT) in oligoprogressive (OP) metastatic breast cancer (MBC), leading to ongoing debate about its role. This retrospective cohort study aimed to investigate whether MDRT can prolong the duration of systemic therapy for at least 6 months in patients with OP MBC. We found that 60% of patients with OP MBC remained on the same systemic therapy for at least 6 months following MDRT, which suggests that MDRT may help prolong the duration of systemic therapy for select patients.

Background: Clinical trials have shown mixed results regarding the benefit of metastasis-directed radiation therapy (MDRT) in oligoprogressive (OP) metastatic breast cancer (MBC), leading to ongoing debate about its role. This study aimed to investigate whether MDRT can prolong the duration of systemic therapy for ≥6 months in patients with OP MBC. Methods: This retrospective cohort study included patients with MBC who received MDRT for OP disease between December 2017 and March 2023. Patients who received MDRT to the brain were excluded. Medical records were reviewed through July 2024. The primary endpoint was the proportion of patients remaining on the same systemic therapy for ≥6 months post-MDRT. Results: In total, 52 patients with OP MBC treated with MDRT were included, with 36 (69%) with HR+/HER2- disease, 10 (19%) with HER2+ disease, and 6 (12%) with TNBC. Among the 47 patients with follow-up data available, 28 (60%) remained on their systemic therapy at 6 months, including 65% (22/34) of patients with HR+/HER2- disease, 56% (5/9) with HER2+ disease, and 25% (1/4) with TNBC (p = 0.30). Among the 38 patients with a follow-up time of at least 1 year post-MDRT, 47% (18/38) remained on the same systemic therapy. The median time to next systemic therapy and median PFS were 6.9 months (95% CI, 5.7–14.7) and 6.2 months (95% CI, 4.1–9.7), respectively. Conclusions: Over half of patients with OP MBC remained on the same systemic therapy for at least 6 months following MDRT, which suggests that MDRT may help prolong systemic therapy duration for select patients.