Concurrent Lapatinib With Brain Radiation Therapy in Patients With HER2+ Breast Cancer With Brain Metastases: NRG Oncology-KROG/RTOG 1119 Phase 2 Randomized Trial

Lapatinib plus whole brain radiation therapy (WBRT) or stereotactic radiosurgery (SRS) was hypothesized to improve the 12-week intracranial complete response (CR) rate compared with either option of radiation therapy (RT) alone for patients with brain metastases (BM) from human epidermal growth factor receptor 2-positive (HER2+) breast cancer.This study included patients with HER2+ breast cancer with ≥1 measurable, unirradiated BM. Patients were randomized to WBRT (37.5 Gy/3 wk)/SRS (size-based dosing) ± concurrent lapatinib (1000 mg daily for 6 weeks). Secondary endpoints included objective response rate (ORR), lesion-specific response, central nervous system progression-free survival, and overall survival.From July 2012 to September 2019, 143 patients were randomized, with 116 analyzable for the primary endpoint. RT + lapatinib did not improve 12-week CR (0% vs 6% for RT alone, 1-sided P = .97), or ORR at 12 weeks. At 4 weeks, RT + lapatinib showed higher ORR (55% vs 42%). Higher graded prognostic assessment and ≤10 lesions were associated with higher 12-week ORR. Grade 3 and 4 adverse event rates were 8% and 0% for RT and 28% and 6% for RT + lapatinib.The addition of 6 weeks of concomitant lapatinib to WBRT/SRS did not improve the primary endpoint of 12-week CR rate or 12-week ORR. Adding lapatinib to WBRT/SRS showed improvement of 4-week ORR, suggesting a short-term benefit from concomitant therapy.