Staging Classifications of Colorectal Liver Metastases

Abstract

The present status of staging classifications of colorectal liver metastases (CRLM) is summarized. Among prognostic factors published for CRLM undergoing liver resection, the most important variables were maximum size and number of CRLM, primary regional lymph node metastasis, and preoperative carcinoembryonic antigen level. In 2017, the eighth TNM cancer staging system of the Union for International Cancer Control and the American Joint Committee on Cancer introduced a new subdivision of M1 classification of colorectal carcinomas: liver-only CRLM, metastasis to multiple sites or organs including CRLM without peritoneal metastasis, and CRLM with peritoneal metastasis were classified into M1a, M1b, and M1c, respectively. Several classification systems and validation studies were introduced after the beginning of modern chemotherapy. Tumor Burden Score (TBS) utilized a continuum of tumor size and number, indicating continuous prognostic stratification. Overall survival was well separated by zones 1–3. The Memorial Sloan-Kettering Cancer Center-Clinical Risk Score (MSKCC-CRS) provided a statistically significant stratification of patients with regard to overall and recurrence-free survival; however, modified MSKCC-CRS, including predictive markers of disease-free interval, number of CRLM, and CEA level with RAS mutation status outperformed the traditional one. The Iwatsuki score and the Nagashima score also had partial predictive value and was particularly evident for patients in high-risk groups. (K)-RAS and BRAF mutations were also prognostic biomarkers of CRLM. The Beppu nomogram for CRLM undergoing upfront hepatectomy and the Imai nomogram for CRLM after conversion therapy was introduced. Surprisingly, node-positive primary, large number of CRLM at hepatectomy, high CA 19−9 level at hepatectomy, and extrahepatic metastasis were common prognostic factors. With progress in systemic chemotherapy and surgical techniques for liver resection, the appropriate staging classification for CRLM has been changing. A staging classification system is required limited to CRLM patients fit for the era of multidisciplinary treatment.