Session Item

Treatment of metastatic breast cancer is mostly based on systemic therapy, while the exact role of radiotherapy is uncertain. During SBRT fewer fractions are used, shorter and faster treatment is more convenient for patients, moreover higher doses are potentially more effective. There is a greater emphasis not only on the effects of oncological treatment but also on the quality of life after the treatment is finished. In this context, radiotherapy may be important in the management of patients with metastatic breast cancer ameliorate clinical outcomes with limited toxicity.

We aimed to assess the effect of stereotactic body radiotherapy (SBRT) on survival, oncological outcomes, in patients with one to five oligometastatic lesions, and the potential delay to subsequent systemic therapy introduction or change (ST).

Out of 247 metastatic breast cancer patients undergoing SBRT (1-5fx, df>4Gy), treated between 2014 and 2020, 69 patients with oligometastatic disease with total dose ≥ 24 Gy were included in our single-institution study. Survival analysis was performed using the Kaplan-Meier method with log-rank test being used for evaluation of significance.

Majority of patients had single metastatic foci (57%), 2 (28%), 3 (10%), 4 (4%), 5 (1%). The most common site of metastases was bone 61%, remaining included lung 19% liver 19%, lymph nodes 1%.  Total dose ranged from 24 to 60 Gy, usually delivered in 3 fractions 89% (1-5 fx). Systemic therapy before SBRT was applied 88% of the patients within this group hormonal therapy 74%, chemotherapy 30%, targeted therapy 17%. Also 83% got systemic therapy during SBRT mostly hormonal therapy 73%, chemotherapy 7%, targeted therapy 12%.  Median follow-up was 28 months (range 2-68), with 67% of patients being alive at the time of analysis. Median time from primary treatment to SBRT was 2.7 years (range 9 mts - 18 years). Median time to further systemic therapy after SBRT was 13 months (1.3-55.5). The 1-, 3-, and 5-year OS were 94%, 64%, 62%, respectively. There was a trend that patients with bone metastases had better LC (p=0.09) and OS (p=0.08). In majority of patients as the first site of failure further distant metastases outside the irradiated volume was found. 1y LC was 84%, 3y was 75%, there were no LC after 25 mts. 1 year MFS was 60%, 3y was 30%, all first dissemination after SBRT had place before 27 mts. 1y, 3y, 5y FFST (freedom from ST) after SBRT were 76%, 39%, and 18%. Majority of patients got ST at the time of disease progression, median time to ST was 1.3 mts, but there were also patients with up to 42 mts FFST after progression. Those who did not get ST at the time of progression were treated with radiotherapy up to 13 courses.

The use of radical radiation therapy to metastatic sites in oligometastatic breast cancer patients can be considered a valuable option and recommended to the appropriate candidates.