Consensus molecular subtypes (CMS) as prognostic and predictive biomarkers 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).

3537 Background: Consensus molecular subtypes (CMS1-4) of colorectal cancer were evaluated as prognostic and predictive biomarkers in the PANAMA trial. PANAMA compared maintenance therapy with panitumumab (Pmab) and fluorouracil/folinic acid (FU/FA) vs. FU/FA alone after Pmab-FOLFOX induction therapy in RAS wildtype mCRC. Methods: Gene expression was measured after mRNA isolation in 179 of 248 patients of the full analysis set. The analysis was conducted using a customized Nanostring PanCancer Progression Panel. The original CMS classifier was re-derived for Nanostring data using a multinomial regression analysis.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 Chi-square-test. Results: Prevalence of CMS was: CMS1, n = 15 (8.4 %); CMS2, n = 82 (45.8 %); CMS3, n = 20 (11.2 %) and CMS4, n = 62 (34.6 %). A prognostic impact of CMS regardless of treatment was not evident for PFS (p = 0.245) and OS (p = 0.169), but for ORR (p = 0.022), with CMS1 and CMS3 being associated with unfavourable efficacy during maintenance therapy. Potential predictive effects of CMS were observed in patients with CMS2 and CMS4 tumours. In CMS2 and CMS4 tumours, ORR was significantly higher when treated with Pmab-FU/FA in maintenance therapy (CMS2: 56.5% vs 30.6%, p = 0.026; CMS4: 55.6% vs. 28.6%, p = 0.040). In patients with CMS2 mCRC, this translated into a significant effect on PFS (Hazard ratio: 0.61 (95% CI 0.38 – 0.99) p = 0.046 (Table). Conclusions: CMS have limited prognostic impact for pmab-based maintenance therapy. However, CMS2 and CMS4 are positively associated with Pmab efficacy during maintenance therapy in the PANAMA trial. Further trials are necessary to confirm these results. [Table: see text]