CTNI-05. NRG ONCOLOGY / RTOG 1119: PHASE II RANDOMIZED STUDY OF WHOLE BRAIN RADIOTHERAPY / STEREOTACTIC RADIOSURGERY WITH CONCURRENT LAPATINIB IN PATIENTS WITH BRAIN METASTASES FROM HER2-POSITIVE BREAST CANCER

Abstract Trastuzumab/pertuzumab improved outcomes for patients (pts) with HER2+ breast cancer. Increased survival coupled with limited blood-brain barrier (BBB) penetration of these agents apparently contributes to increased incidence of brain metastases (BM). Lapatinib (L) crosses the BBB and demonstrates activity against BM. Based upon pre/early clinical data, it’s hypothesized that L + whole brain radiotherapy (WBRT) or Stereotactic Radiosurgery (SRS) would improve intracranial control compared to WBRT/SRS (RT) alone. This randomized phase II trial included HER2+ breast cancer pts with ≥ 1 measurable, unirradiated parenchymal BM. Pts were randomized 1:1 to WBRT (37.5 Gy/3 weeks) or SRS +/- concurrent L (1000 mg dailyx6 weeks), andwere stratified by graded prognostic assessment (GPA), use of non-CNS penetrating anti-HER2 therapies, and previous SRS/resection. The primary endpoint was intracranial complete response (CR) rate 12weeks (wk) after RT. Secondary endpoints included objective response rate (ORR), lesion-specific response rate, CNS progression-free survival, and overall survival. 114 of 143 pts were evaluable for 12-wk CR (52 RT, 62 RT+L). Rate of grade 3 and 4 adverse events were 8% and 0% for RT and 29% and 6% for RT+L. 92% and 90% pts received concurrent and adjuvant L per protocol/acceptable variation. There were no significant differences in 12 or 4wk CR rates (p=0.97 and p=0.77); 5.8% and 0% at 12wk and 3.6% and 1.5% at 4wk for RT and RT+L, respectively. The ORR at 4 wk was 42% and 56% (p=0.059, RECIST), 40% and 58% (p=0.027, WHO) in the RT and RT+L, respectively. Although the addition of lapatinib to WBRT/SRS did not improve the 12wk CR rate, it showed meaningful clinical benefit by demonstrating a trend toward improvement of 4 wk ORR. Results of ongoing central review of MRIs using RECIST1.1, WHO and RANO-BM criteria including secondary endpointswill be reported. Support: NCI grants U10CA180868, U10CA180822, UG1CA189867, and Novartis