ESTRO 2024 - Abstract Book

S726

Clinical - Breast

ESTRO 2024

It is well known that patients with oligometastaic breast cancer (OMBC) in majority of cases have good local control of irradiated metastatic lesions, but they often experience further disease progression usually in form of new distant metastases. The aim of our study was to evaluate outcome of stereotactic body radiotherapy (SBRT) applied in OMBC. We evaluated variable factors before SBRT in patients who achieved local (LC) and distant control (DC) of the disease (group 1) and in those with disease progression after SBRT (group 2).

Material/Methods:

For our retrospective analysis we analysed patients diagnosed with OMBC treated in our center between 2009-2022, 353 were treated with SBRT with total dose ≥ 24 Gy, delivered in 1 -5 fx, with more than 4 Gy per fraction, from this group we selected 71 with up to 5 extracranial metastatases who were treated for a total of 94 metastatic lesions. Survival analysis was performed using the Kaplan-Meier method with log-rank test being used for evaluation of significance.

Results:

Among all 71 selected patients the 1-, 3-, and 5-years OS were 94%, 64% and 55% respectively. 1 year MFS was 63%, 3y was 33% and 5y was 28%. 1y PFS was 55%, 3 years 30% and 5 years 27%. Majority of patients have very good local control – 1 year 95%, 2 and 5 years 88%. Patients with synchronous oligometastatic disease had better OS (p=0.02) and PFS (p=0.006) than patients with metachronous disease. Group 1 consists of 26 patients (with 32 irradiated metastases) and group 2 consists of 45 patients (with 62 irradiated metastases). In both groups majority of patients were HR+/HER2(-), but they predominated in group 1 (69% vs. 51%), similar amount of HR+/HER2(+) patients (15% vs. 16%) and HR-/HER2(+) patients (8% vs. 11%) were in both groups, more TNBC were in group 2 (13% vs. 8%). In group 2 metachronous disease (78% vs. 50%) was more often present. In both groups the most common T stage was T2 (38% and 36%), more T1 patients were in group 1 (31 vs. 22%) but also T4 (19% vs. 15.5%). There were greater volumes of tumor foci in group 2 – median 6.85 cm3 (range 0.11 – 82.3 cm3) vs. 3.7 cm3 (range 0.3 – 48.6 cm3) in group 1. There were no differences between age of patients - median age in group 1 was 59 years (range 29 to 83 years) vs. 56 years (range 37-93 years) in group 2. In group 1 irradiated metastases were only newly diagnosed (53%), stable after systemic therapy (12.5%) or regressed after systemic therapy (34.5%) foci, whereas in group 2 apart from new (65%), stable (6%) and regressive (15%) ones, there were also metastases progressing over time and they accounted for 13% of all lesions. In both groups the most common site of metastases were bones (75% in group 1 vs. 66% in group 2), remaining included lung (6% vs. 16%), liver (13% vs. 18%) and lymph nodes (only in group 1 – 6%).

Conclusion:

Using variable clinical factors, we were not able to predict which patient will benefit or not from SBRT. More patient with metachronous disease tends to have worse outcome. Further research is needed to determine this issue.

Keywords: oligometastases, SBRT