AbstractDespite molecular selection, patients (pts) with RAS wildtype mCRC represent a heterogeneous population including diversity in metastatic spread. We investigated metastatic patterns for their prognostic and predictive impact on maintenance therapy with 5‐fluorouracil/folinic acid ± panitumumab. The study population was stratified according to (1) number of involved metastatic sites (single vs multiple organ metastasis), liver‐limited disease vs (2) liver metastasis plus one additional site, and (3) vs liver metastasis plus ≥two additional sites. Kaplan‐Meier method and Cox regressions were used to correlate efficacy endpoints. Single organ metastasis was observed in 133 pts (53.6%) with 102 pts (41.1%) presenting with liver‐limited disease, while multiple organ metastases were reported in 114 pts (46.0). Multiple compared to single organ metastases were associated with less favorable PFS (HR 1.48, 95% CI 1.13‐1.93; P = .004) and OS (HR 1.37, 95% CI 0.98‐1.93; P = .068) of maintenance therapy. While metastatic spread involving one additional extrahepatic site was not associated with clearly impaired survival compared to liver‐limited disease, pts with liver metastasis plus ≥two additional sites demonstrated less favorable PFS (HR 1.92, 95% CI 1.30‐2.83; P < .001), and OS (HR 2.38, 95% CI 1.51‐3.76; P < .001) of maintenance therapy. Pmab‐containing maintenance therapy appeared active in both pts with multiple (HR 0.58; 95% CI, 0.39‐0.86; P = .006) as well as to a lesser numerical extent in pts with single organ metastasis (HR 0.83; 95% CI, 0.57‐1.21; P = .332; Interaction P = .183). These data may support clinical decisions when EGFR‐based maintenance therapy is considered.