Primary tumour resection plus systemic therapy versus systemic therapy alone in metastatic breast cancer (JCOG1017, PRIM-BC): a randomised clinical trial

Background: Several prospective studies have evaluated the benefit of primary tumour resection (PTR) in de novo Stage IV breast cancer (BC) patients, but it remains controversial. We aimed to investigate whether PTR improves the survival of de novo stage IV BC patients.
Methods: De novo stage IV BC patients were enrolled in the first registration and received systemic therapies according to clinical subtypes. Patients without progression after primary systemic therapy for 3 months were randomly assigned 1:1 to systemic therapy alone (arm A) or PTR plus systemic therapy (arm B). The primary endpoint was overall survival (OS), and the secondary endpoints included local relapse-free survival (LRFS).
Results: Five hundred seventy patients were enrolled between May 5, 2011, and May 31, 2018. Of these, 407 were randomised to arm A (N = 205) or arm B (N = 202). The median follow-up time of all randomised patients was 60 months. The difference in OS was not statistically significant (HR 0.86 90% CI 0.69–1.07, one-sided p = 0.13). Median OS was 69 months (arm A) and 75 months (arm B). In the subgroup analysis, PTR was associated with improved OS in pre-menopausal patients, or those with single-organ metastasis. LRFS in arm B was significantly longer than that in arm A (median LRFS 20 vs. 63 months: HR 0.42, 95% CI 0.33–0.53, p < 0.0001). There were no treatment-related deaths.
Conclusions: PTR did not prolong OS. However, it improved local control and might benefit a subset of patients, such as those with premenopausal status or with single-organ metastasis. It also improved local relapse-free survival (LRFS), which is a clinically meaningful outcome in trials of systemic therapy.
Clinical trial registration: UMIN Clinical Trials Registry (UMIN000005586); Japan Registry of Clinical Trials (jRCTs031180151).