(P002) HER2 Status and Site of Metastases Predict Survival for Women Treated With Stereotactic Body Radiation Therapy/Stereotactic Radiosurgery (SBRT/SRS) for Oligometastases

Anthony G. Ricco, Allison Winger, BS, Rachelle M. Lanciano, MD, John Lamond, MD, Deborah Markiewicz, MD, William Ding, MD, Stephen Arrigo, MD, Luther Brady; Sidney Kimmel Medical College, Thomas Jefferson University; Drexel University College of Medicine; Philadelphia CyberKnife

INTRODUCTION: The use of stereotactic body radiation therapy (SBRT) for treatment of breast cancer oligometastases is being studied by the NRG Oncology Group for toxicity (trial BR001) and survival (trial BR002). Outcome data and prognostic factors for breast cancer oligometastases treated with SBRT, however, are lacking in the literature.

METHODS: Between November 2007 and December 2014, a total of 39 women were treated with SBRT/stereotactic radiosurgery (SRS) for oligometastases, defined as < 4 sites of disease. Ninety-seven percent of patients were previously treated with systemic therapy. Median time to SBRT from presentation of metastatic disease was 14.3 months (range: 0–103 mo). SBRT was delivered utilizing the CyberKnife system, with a median dose of 20 Gy (range: 15–60 Gy), a median of 3 fractions (range: 1–5) and 136 beams (range: 68–227), and a median clinical target volume (CTV) of 7.7 cm³ (range: 0.2–135 cm³). Sites of SBRT/SRS (n = 50) included lung (n = 5), bone (n = 14), liver (n = 3), lymph node (n = 6), brain (n = 20), adrenals (n = 1), and chest wall (n = 1). Receptor status included triple-negative (n = 11), human epidermal growth factor receptor 2 (HER2)-positive (n = 11), and estrogen receptor (ER)- or progesterone receptor (PR)-positive + HER2-negative (n = 17). Actuarial/median survival statistics and log-rank P values were calculated.

RESULTS: Median survival following SBRT for the entire group was 14.56 months, with 1-year and 2-year actuarial survival rates of 53.8% and 38.5% respectively. Prognostic factors evaluated for survival included brain vs other sites, Eastern Cooperative Oncology Group performance status 0 vs 1–3, number of metastases 1–2 vs > 2, age ≤ 50 years vs > 50 years, and receptor status triple-negative vs HER2+ vs ER+ or PR+/HER2−. Only brain metastases (P = .18) and HER2+ receptor status (P = .04) reduced median survival from 23.2 months and 20.7 months, respectively, to 10.5 months for both groups.

CONCLUSIONS: We document survival and prognostic factors of SBRT for breast cancer oligometastases in a single institution. Information about the survival benefit of SBRT following chemotherapy awaits the results of the phase II/III NRG BR002 trial.

Proceedings of the 98^th Annual Meeting of the American Radium Society - americanradiumsociety.org