(P019) Predictors of Outcomes in Breast Cancer Patients With Oligometastases

Shefali Gajjar, MD, Arthy Yoga, MD, Isildinha M. Reis, PhD, Youssef Zeidan, MD, PhD, Cristiane Takita, MD;Department of Radiation Oncology, Department of Epidemiology & Public Health, University of Miami/Sylvester Comprehensive Cancer Center; Department of Surgery, University of Miami

BACKGROUND: Oligometastases are hypothesized to represent a potentially curable disease. With the emergence of stereotactic body radiotherapy (SBRT) and stereotactic radiosurgery (SRS), additional treatment options have been presented to patients with limited metastases. Studies have shown that breast cancer patients with oligometastases tend to fare better than patients with oligometastases from other primary sites. However, no studies have examined predictors of outcomes in patients with oligometastatic breast cancer.

MATERIALS AND METHODS: We identified 380 patients treated at our institution with SBRT or SRS from 2010–2014. We retrospectively reviewed the records of 62 patients with metastatic breast cancer. We defined oligometastases as metastases at ≤ 5 distinct clinical sites. Oligometastases were determined by imaging and clinical documentation. Kaplan-Meier curves were used to determine survival after metastasis. A Cox proportional hazards model was used to assess the effect of patient, tumor, and treatment characteristics as predictors of survival after metastases.

RESULTS: There were 30 patients with oligometastases and 32 patients with non-oligometastases. A total of 60% of patients had initial stage I, II, or III disease, while 40% had stage IV. The tumor was estrogen receptor (ER)-positive, progesterone receptor (PR)-positive, and human epidermal growth factor type 2 (HER2)-positive in 63%, 46%, and 20% of oligometastatic patients and in 66.7%, 57%, and 28% of nonoligometastatic patients, respectively. Triple-negative disease was noted in 27% of patients in both arms. Further, 95% received chemotherapy and about 60% received hormonal therapy in both groups. The 5-year survival rate after metastases was 79.6% for oligometastatic vs 45.7% for nonoligometastatic patients. Univariate models showed that the predictors of inferior survival after metastases included: absence of oligometastases (hazard ratio [HR] = 3.39; 95% confidence interval [CI], 1.28–9.19; P = .016), HER2-negative status (HR = 12.42; 95% CI, 1.63–94.56; P = .015), and triple-negative status (HR = 3.61; 95% CI, 1.43–9.07; P = .006). On bivariate analyses, absence of oligometastases remained a significant predictor of worse survival after metastasis: absence of oligometastases (HR = 6.07; 95% CI, 1.56–23.710; P = .009) adjusted for HER2-positive status (HR = 17.55; 95% CI, 2.13–144.84; P = .008) in model 1 and absence of oligometastases (HR = 5.31; 95% CI, 1.54–18.31; P = .008) adjusted for triple-negative status (HR =3.65; 95% CI, 1.43–9.29; P = .007) in model 2.

CONCLUSION: Our study showed that oligometastatic breast cancer patients have improved 5-year survival after metastases compared with non-oligometastatic patients. In patients with oligometastases and HER2-positive disease or without triple-negative disease, survival after metastases was superior. Further studies are needed to identify a favorable subset of patients with oligometastases who would benefit from aggressive therapy.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org