The response of colorectal adenocarcinoma liver metastases to perioperative chemotherapy can be assessed histologically in partial hepatectomy specimens. Necrosis in this scenario may represent a lack of treatment effect or a therapeutic response to chemotherapy. This study sought to validate the histologic classification of necrosis into 2 types: usual necrosis (UN) representing an absence of treatment effect, and infarct-like necrosis (ILN) representing a therapeutic response to chemotherapy. Tumor regression grade (TRG) is a previously described prognosticating method that estimates tumor replacement by fibrosis. We incorporated ILN into a modified TRG (mTRG) and compared its performance as a prognostic factor against TRG. A retrospective clinical and histologic review was undertaken of all partial hepatectomies performed for colorectal liver metastases at our center between 2004 and 2010. Clinicopathologic features were compared between the 2 types of necrosis, including survival stratified by TRG and mTRG. A total of 109 cases were reviewed, with 46 patients receiving perioperative chemotherapy. ILN was identified in 12 cases, and all of these cases were associated with perioperative chemotherapy. ILN was significantly associated with perioperative treatment with bevacizumab. In patients receiving perioperative chemotherapy, those with ILN had superior disease-free survival compared with those with UN (P=0.047). mTRG1 to 2 scores were associated with significantly better survival compared with mTRG3 to 5 scores. In contrast, use of TRG did not demonstrate a significant difference in disease-free and overall survival. ILN represents a form of treatment effect and should be distinguished from UN. A modified grading system that incorporates ILN may enhance the prognostic utility of TRG.