The Role of Stereotactic Body Radiotherapy in Oligoprogressive Malignant Disease (RADIANT): Oncologic Outcomes From a Phase 2 Nonrandomized Controlled Trial

Purpose

In oligoprogressive (OP) cancer, there are a limited number of metastatic areas progressing on a background of stable or responding to widespread cancer. Although the standard of care for OP is changing systemic therapy (ST), stereotactic body radiation therapy (SBRT) is being explored as an alternative local therapy targeting the sites of progression.

Methods and Materials

RADIANT (NCT04122469) was a single-center phase 2 study of patients with metastatic genitourinary (GU), breast, and gastrointestinal (GI) cancers, receiving ST for ≥3 months, with radiographic OP disease in ≤5 sites. Patients received SBRT for all OP disease in 1 to 5 fractions and were maintained on ST. The primary endpoint was the cumulative incidence of change in ST, which was estimated using the Aalen-Johansen method. Secondary endpoints included progression-free survival (PFS) and overall survival estimated using the Kaplan-Meier method, as well as toxicity and health-related quality of life. Comparisons between diagnosis groups were done using the log-rank test. A 2-sided p value <.05 was considered statistically significant.

Results

Seventy patients were analyzed, with a median age of 69 years; 32 patients (46%) were women; the median number of lines of prior ST was 3. Primary sites were GU (n = 32; 46%), breast (n = 23; 33%), and GI (n = 15; 21%). The median follow-up was 12.3 months (IQR, 8.2-21.6 months). At 1 year, change in ST occurred in 47% (95% CI, 36%-61%) (GU 45%, breast 41%, and GI 60%; p = .23). PFS at 1 year was 32% (95% CI, 23%-45%), and median PFS was 4.7 months (95% CI, 3.8-8.1) (GU 4.8, breast 6.5, and GI 3.2), which significantly differed by disease type (p = .006). Overall survival was 75% at 1 year (95% CI, 65%-87%), which significantly differed between cancer types (GU 86%, breast 96%, and GI 22%; p < .001). The cumulative incidence of late grade ≥2 toxicity was 1.2%, with 1 patient experiencing late grade 3 toxicity and no grade 4 to 5 acute or late toxicities. Health-related quality of life declined from the mean (SD) of 66.9 (20.2) at baseline to 60.5 (22.2) at 6 months, which did not meet the threshold for a minimal clinically important difference.

Conclusions

SBRT for OP metastases delayed change in ST in approximately half of patients, warranting investigation in randomized trials.