Significance of liver metastasis volume in breast cancer patients treated with stereotactic body radiotherapy.

PURPOSE: This study analyzed the impact of liver metastasis (LM) volume on treatment outcomes in breast cancer (BC) patients treated with stereotactic body radiotherapy (SBRT).

METHODS

This single-institution retrospective analysis included 40 oligometastatic (≤ 5 metastases) BC patients with 58 liver metastases treated with SBRT between April 2013 and March 2021. The prognostic factors for local control (LC), overall survival (OS), and progression-free survival (PFS) rates were assessed.

RESULTS

Median follow-up time was 28.1 months. Isolated and solitary LM were seen in 26 (65%) and 24 (60%) patients, respectively. Median time to disease recurrence was 10.7 months post liver SBRT. The 2‑year OS, PFS, and LC rates were 71.4%, 27.5%, and 86.8%, respectively. In univariate analysis, patients with a gross tumor volume (GTV) of ≤ 6 cc and a planning target volume (PTV) of ≤ 38 cc demonstrated a significantly better median OS than those with GTV > 6 cc and PTV > 38 cc. In multivariate analysis, the predictive factors for worse OS were GTV > 6 cc (HR = 3.07 [95% CI, 1.14-8.22; p = 0.03]) and PTV > 38 cc (HR = 5.91 [95% CI, 1.92-18.21; p = 0.002]). No significant factor for PFS was found. Only 2 patients experienced rib fracture at 4 and 6 months post treatment, and 1 patient had a grade II duodenal ulcer.

CONCLUSION

Liver SBRT is an effective and safe treatment option for oligometastatic BC patients with excellent LC, promising survival, and limited toxicity. Patients with smaller tumors displayed better OS than their counterparts, validating the effectiveness of a local treatment for this group.