Neratinib plus Cetuximab in Quadruple WT (KRAS, NRAS, BRAF, PIK3CA) Metastatic Colorectal Cancer Resistant to Cetuximab or Panitumumab: NSABP FC-7, A Phase Ib Study.

Purpose: In metastatic colorectal cancer (mCRC), HER2 (ERBB2) gene amplification is implicated in anti-EGFR therapy resistance. We sought to determine the recommended phase II dose (RP2D) and efficacy of neratinib, a pan-ERBB kinase inhibitor, combined with cetuximab, in patients with progressive disease (PD) on anti-EGFR treatment. Experimental Design: Twenty-one patients with quadruple-wild-type, refractory mCRC enrolled in this 3+3 phase-Ib study. Standard dosage cetuximab was administered with neratinib at 120mg, 160mg, 200mg, and 240mg/day orally in 28-day cycles. Samples were collected for molecular and pharmacokinetic studies. Results: Sixteen patients were evaluable for dose-limiting toxicity (DLT). 240mg was determined to be the RP2D wherein a single DLT occurred (1/7 patients). Treatment-related DLTs were not seen at lower doses. Best response was stable disease (SD) in 7/16 (44%). HER2 amplification (CISH) was detected in 2/21 (9.5%) treatment-naive tumors and 4/16 (25%) biopsies upon trial enrollment (post-anti-EGFR treatment and progression). Compared to matched enrollment biopsies, 6/8 (75%) blood samples showed concordance for HER2 CNV in cfDNA. Five SD patients had HER2 amplification in either treatment-naive or enrollment biopsies. Examination of gene-expression, total protein, and protein phosphorylation levels showed relative upregulation of ≥2 members of the HER-family receptors or ligands upon enrollment versus matched treatment-naive samples. Conclusions: The RP2D of neratinib in this combination was 240mg/day, which was well tolerated with low incidence of G3 AEs. There were no objective responses; SD was seen at all neratinib doses. HER2 amplification, detectable in both tissue and blood, was more frequent post-anti-EGFR therapy.