Stereotactic Ablative Radiotherapy (SABR) in Oligometastatic and Oligoprogressive Gynecologic Cancers: Clinical Outcomes of a Single Institution Analysis

Abstract

The role of stereotactic ablative radiotherapy (SABR) for gynecologic malignancies has not been clearly defined despite recent clinical uptake. This study evaluates the outcomes of SABR in patients with metastatic gynecologic cancer at a single institution. Patients with gynecologic cancers treated from 2009-2019 were extracted from an institutional SABR database. Descriptive statistics were used to report patient and treatment characteristics, toxicity and chemotherapy-free interval. Local recurrence free survival (LRFS), distant progression-free survival (DPFS), and overall survival (OS) probabilities were calculated using Kaplan-Meier methods. The relationship of primary site, tumor grade, dose of radiotherapy, and disease-free interval (DFI) to LRFS and DPFS were assessed using Cox regression methods for multivariable analysis (MVA). One hundred nine lesions in 77 patients with gynecologic cancer were treated with SABR. Median age was 63 and follow up after SABR was 16.4 months (1-79.6). Patients were treated with SABR for oligoprogressive disease (n = 58), oligometastatic disease (n = 34), or for local progression in critical areas (n = 17). Primary site included cancers of the endometrium (n = 36), cervix (n = 19), ovary (n = 15), and vulva or vaginal (n = 7). Median DFI was 22.3 months (1.6-143.3) from diagnosis to metastasis. Treatment was delivered to lesions in the lung (n = 25), pelvis (n = 23) spine (n = 17), para-aortic (n = 16) and distant nodes (n = 7), abdominal organs (n = 13), and bone (n = 8). Radiotherapy doses ranged from 25-60Gy (median 35Gy) in 2-5 fractions. Patients had between 1 and 6 lesions treated. Thirteen lesions recurred locally (11.9%) at a median of 7.6 months (range 0.5-17.6), and 76% of patients eventually had a distant recurrence after SABR. Median DPFS was 7.8 months (95% CI 3.6-11.9), and OS 31.5 months (95% CI 12.2-45.7). At 2 years, LRFS was 77.6%, DPFS was 19.6%, and OS was 51.9%. Thirty-two patients eventually required chemotherapy at median 6 months (range 1-37). There were no grade 3-5 acute or late toxicities reported. On MVA, primary site, tumor grade, dose of radiotherapy and DFI were not significantly associated with LRFS or DRFS. This cohort of patients had excellent LRFS and DPFS when treated with SABR for oligoprogressive, oligometastatic and locally progressive disease. SABR also has the potential to delay time to chemotherapy in patients with gynecologic cancers. Prospective multi-center trials will be critical to establish which primary disease sites and characteristics procure the greatest benefit from SABR use, to delineate optimal dose regimens, and to define the ideal time to implement SABR with other oncologic treatments.