Primary Tumor Histology Affects Oncological Outcomes Independently of the Anatomical Extent of Disease in Colorectal Liver Metastasis

INTRODUCTION: Growing evidence indicates the prognostic importance of the crosstalk between cancer cells and stroma through the induction of epithelial-mesenchymal transition (EMT). This study aimed to clarify the prognostic value of evaluating primary tumor histology with the anatomical extent of disease in patients with colorectal liver metastasis (CRLM). METHODS: Prognostic analyses were performed in 411 CRLM patients who underwent hepatectomy at two institutions. Tumors were graded into one of three histological categories based on integrated assessment of EMT-associated histology (Histology(EMT)) in primary tumors, i.e., poorly differentiated clusters (PDCs) and desmoplastic reaction (DR). RESULTS: A prognostic grouping system for the anatomical extent of disease (N stage, liver metastasis number and size, and extrahepatic disease; Grade(anatomical)) stratified patients into three groups with different five-year relapse-free survival (RFS) rates after hepatectomy: A, 31% (191 patients); B, 15% (124 patients); and C, 6% (96 patients; P < 0.0001). Histology(EMT) (A, G1 PDC and mature-type DR; C, G3 PDC and immature-type DR; and B, others) identified 49, 120, and 242 patients with 46%, 5%, and 22% five-year RFS, respectively (P < 0.0001). Among prognostic factors, the Akaike information criterion was most favorable in Grade(anatomical), followed by Histology(EMT). Multivariate analysis demonstrated that these two factors independently impacted RFS; two-year RFS after hepatectomy in different patient groups had a wide range (10%-76%). CONCLUSIONS: Histological assessment of dedifferentiation and the stromal environment of primary tumors contributed to effective risk stratification of early relapse after hepatectomy, which could be useful to determine clinical management for CRLM patients.