Non-size-based response criteria to preoperative chemotherapy in patients with colorectal liver metastases: the morphologic response criteria.

Since the introduction of biologic agents, increasing data have suggested that conventional size-based RECIST criteria are not accurate in the assessment of response to therapy and non-size-based changes in tumor morphology can be a surrogate marker for assessment of chemotherapeutic effect. The morphologic response criteria are recently introduced, non-size-based criteria for patients undergoing chemotherapy for colorectal liver metastases (CLM). These novel criteria predict pathologic response and long-term survival of patients treated with preoperative chemotherapy, with or without bevacizumab, independent of their RECIST response. They have been validated in patients with resectable and unresectable CLM. These criteria are difficult to apply in small metastases and can be used as an adjunct to RECIST in the assessment of response to preoperative chemotherapy.