[A prognostic nomogram for metastasized colorectal cancer patients treated with cetuximab]

Objective: To identify the prognostic factors in metastatic colorectal cancer (mCRC) patients treated with cetuximab and establish a prognostic nomogram and validate its accuracy. Methods: A retrospective case-control study was conducted. Patients were selected as following criteria: patients with metastatic colorectal cancer(mCRC), which primary site confirmed by pathology and metastatic lesions confirmed by CT or MRI with at least one measurable and evaluable target lesion; patients' expected survival longer than 3 months; Eastern Cooperative Oncology Group (ECOG) score between 0 to 2; patients have signed informed consent; both KRAS and NRAS genes were wild-type; and at least 2 cycles of cetuximab combined with chemotherapy as the first-line regimen. Patients who met the following criteria were excluded: patients with incomplete clinicopathological and follow-up data; patients with severe diseases of vital organs such as heart, brain, lung, kidney, or other advanced malignant tumors; patients without informed consent. According to the above criteria, clinicopathological data of 95 patients with mCRC admitted in the Department of Medical Oncology, the Second Affiliated Hospital, Zhejiang University School of Medicine for first-line treatment with cetuximab from January 2010 to January 2017 were analyzed retrospectively. The Cox proportional hazards model was used to analyze the clinicopathological factors to determine the independent prognostic factors for progression-free survival(PFS). The R software was adopted to establish a prognostic nomogram model. Then, the nomograms of 6-month, 12-month and 18-month progression-free survivals (PFS) were drawn, and compared with the reality. The internal validation and accuracy of the nomogram were determined by the Bootstrap method and also the calculated concordance index (C-index). Results: The median follow-up time was 16.5 (2-43) months and the median PFS was 8.5 months. PFS at 6-,12- and 18-month was 73.7%, 35.8%, and 17.9%, respectively. ECOG score of 1-2 (HR=5.733, 95% CI:2.408-13.649, P<0.001), primary tumor was located in the ileocecal region (HR=5.880, 95% CI:1.645-21.023, P=0.006), Ki-67 index ≥45% (HR=3.574,95% CI:1.403-9.108,P=0.008), baseline D-dimer level ≥345 mg/L (HR=2.536,95% CI:1.531-7.396, P=0.012), NLR≥2.8 (HR=5.573,95% CI:2.107-14.740,P=0.001) and the combined treatment for FOLFOX (HR=0.465, 95% CI: 0.265-0.817, P=0.008) were independent risk factors for PFS of mCRC patients (all P<0.05). These independent risk factors were taken into account to construct a nomogram prediction model. The bootstrap method was used to perform internal validation, and the C-index of the nomogram prediction model in this study was 0.67 (95% CI: 0.64~0.71). The 6-, 12- and 18-month PFS predicted by the nomogram were consistent with the actual values. Conclusion: The nomogram model constructed by ECOG score, primary tumor site, Ki-67 index, baseline D-dimer level, baseline NLR and chemotherapy regimen may predict the prognosis of mCRC patients treated with cetuximab more accurately and individually, which can assist clinicians in making treatment decisions.