Abstract OT2-20-01: Rogaratinib, palbociclib and fulvestrant in advanced hormone receptor-positive (HR+), FGFR1/2-positive breast cancer: Phase I trial plus an expansion cohort
Authors: Pernas Sonia , Hernando Cristina , Bermejo Begoña , Martinez-Jañez Noelia , Saenz Jose A García , Morales Serafin , Manso Luis , Silva Jorge , Guerra Juan A , Malon Diego , Mouron Silvana , Caleiras Eduardo , Quintela-Fandino Miguel 
Published: March 2022

Background: Novel therapies are needed upon progression to first-line CDK4/6 inhibitor (CDKi) plus endocrine therapy in advanced HR+ breast cancer. One frequent alteration driving resistance to CDKi plus hormones is FGFR1/2 amplification/overexpression. We have demonstrated that a combined assay of RNAScope and FISH, detecting RNA overexpression and genomic amplification of FGFR1/2, captures more FGFR-aberrant cases than either test alone. When these alterations exist, the triple estrogen receptor (ER), CDK4/6 and FGFR1/2 blockade is able to revert acquired resistance to CDKi (Breast Cancer Res; 23:21-37; 2021). Rogaratinib is a selective FGFR1-4 kinase inhibitor with significant activity in FGFR-aberrant malignancies. In this trial we will test the safety of the triple blockade combining fulvestrant, palbociclib and rogaratinib. We will also study its role as a resistant-reversion combo for FGFR1/2-positive, HR+ patients progressing to a CDK4/6 inhibitor plus aromatase inhibitor (AI) in the first-line metastatic setting. Trial design: Single-arm, prospective, multicentric, open-label, phase I dose-escalation trial. Patients will be pre-screened for amplification and/or overexpression of FGFR1/2 by FISH and RNAScope, during their first-line treatment. Positive patients will start treatment: on day 1, patients will receive rogaratinib q12 hours. On day 2, patients will continue on rogaratinib, receive fulvestrant (500 ug IM) and start on palbociclib (100 mg/day on days 1-21). A second fulvestrant dose (500 ug) will be administered in day +15. The first cycle will be 29 days, followed by 28-day cycles (continuous rogaratinib q12 hours days 1-28, fulvestrant 500 ug day 1, and palbociclib 100 mg/day days 1-21). Rogaratinib will be escalated, starting on 400 mg/bid in 200 mg/bid increments, following a classic 3+3 schedule. Patients experiencing ≤ grade 1 tolerable side effects as the greatest toxicity will be allowed to escalate palbociclib to 125 in cycle 2. A full pharmacokinetic profile and pharmacodynamics (plasma FGF23 and phosphate levels) will be performed on days 1 and 15 of cycle 1. The impact of the triple combination in immunodynamics will be assessed on PBMCs on days 2 and 15. Ten additional HR+, FGFR1/2 + patients will be accrued at the RP2D in an expansion cohort to study efficacy. RECIST 1.1 and NCI CTC AE V 5.0 criteria will be used for assessing disease control (q8 weeks) and toxicity. Eligibility criteria: Pre-screening: Women &gt;18 year old diagnosed with advanced, non-curable HR+ breast cancer; 2) who are receiving first-line treatment with an AI and any oral CDKi; 3) Adequate organ function. Full screening: 4) Positivity for amplification (FISH ratio&gt;2.2) and/or overexpression (RNAScope score of 3+ or 4+) of either FGFR1/2. 5) PD to first-line AI + CDKi within the last 28 days. 6) Recovery from previous toxicity to &lt; tolerable G2. Specific aims: Primary: 1) To determine RP2D of the triple combination of fulvestrant, palbociclib and rogaratinib. 2) To assess the safety and toxicity of the former combination 3) To study the pharmacokinetics, pharmacodynamics and immunodynamics of the triplet. Secondary: 1) To determine the PFS time and 6-month PFS rate of the triplet in FGFR1/2 amplified/overexpressed patients AI + CDKi doublet. Statistical methods: We will follow a 3+3 escalation schedule; thus, the minimum and maximum number of patients for the dose-escalation phase will range between 6 and 18 (no escalation planned beyond 800 mg/bid rogaratinib). Ten additional patients will be accrued in the expansion cohort (N=28). The anticipated rate of positive screening is 40%; thus, we will screen approximately 70 patients. . Present accrual/target accrual: 55/70 screened; 16 FGFR1/2-positive (of 28 planned); 2 accrued and treated.

Citation Format: Sonia Pernas, Cristina Hernando, Begoña Bermejo, Noelia Martinez-Jañez, Jose A García Saenz, Serafin Morales, Luis Manso, Jorge Silva, Juan A Guerra, Diego Malon, Silvana Mouron, Eduardo Caleiras, Miguel Quintela-Fandino. Rogaratinib, palbociclib and fulvestrant in advanced hormone receptor-positive (HR+), FGFR1/2-positive breast cancer: Phase I trial plus an expansion cohort [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-20-01.