Combined amphiregulin and epiregulin expression as a prognostic and predictive biomarker of panitumumab (Pmab), fluorouracil, and folinic acid (FU/FA) or FU/FA maintenance therapy following Pmab+FOLFOX induction in RAS wildtype metastatic colorectal cancer (mCRC): PANAMA trial (AIO-KRK-0212).

Abstract

3528 Background: mRNA expression of amphiregulin ( AREG) and epiregulin ( EREG) as ligands of the epidermal growth factor receptor (EGFR) were associated with response to anti-EGFR directed antibodies in metastatic colorectal cancer (mCRC). Their role for maintenance treatment remained unclear yet and was investigated in the PanaMa trial (panitumumab (Pmab) and fluorouracil/folinic acid (FU/FA) vs. FU/FA alone after Pmab+FOLFOX induction therapy in RAS wild-type mCRC). Methods: Gene expression was measured after mRNA isolation in 196 of 248 patients of the full analysis set. The analysis was conducted using a customized Nanostring PanCancer Progression Panel. AREG and EREG mRNA expression was dichotomized by median. High combined expression was defined as mRNA expression of AREG and EREGequal or above the median. Median progression-free (PFS) and overall survival (OS) since start of maintenance were estimated by Kaplan-Meier-method and Cox-regression, using the log rank test. Objective response rates (ORR) of maintenance therapy were compared by Fisher’s exact test. Treatment interaction was tested by Cox regression. Results: In 196 patients with available mRNA expression data, high AREG, EREG and combined AREG / EREG expression were observed in 103 (52.6%), 97 (49.5%) and 84 (42.9%), respectively. Regardless of treatment, high combined AREG / EREG expression was associated with prolonged PFS (7.7 vs. 5.8 months, HR 0.69 (95% CI 0.51 – 0.93), P=0.016), OS (30.1 vs. 24.4 months, HR 0.58 (95% CI 0.41 – 0.82), P=0.002) and increased ORR of maintenance treatment (39.3% vs. 28.6%, P=0.13), compared to low expression. Tumors with high combined AREG / EREG expression were associated with numerical longer PFS, OS and higher ORR when treated with Pmab+FU/FA maintenance (Table). Significant interaction of combined AREG / EREG expression with treatment was observed in terms of PFS ( P=0.003) and OS ( P=0.016). Conclusions: Combined AREG and EREG mRNA expression was confirmed as prognostic biomarker for mCRC patients receiving maintenance treatment. Efficacy of maintenance treatment might potentially be higher for Pmab+FUFA maintenance in mCRC with high combined AREG / EREG expression in the PanaMa trial. [Table: see text]