Histopathological regression of gastric adenocarcinoma after neoadjuvant therapy: a critical review

As the perioperative chemotherapy has been widely implemented on the management of gastric cancer patients, heterogeneity of clinical outcomes has been evidenced in parallel to different histopathological regression pattern of gastric cancer cells. Tumor histological response to preoperative therapy has been graded by various systems in order to categorize the amount of regressive changes induced by chemotherapy in relation to residual tumor. In this context, tumor regression grading (TRG) systems might provide important prognostic information as the variety of tumor response may imply on different clinical outcomes with impact in survival rates. Moreover, gastric cancer behavior varies enormously upon individual factors such as histological classification and tumor anatomic site of involvement that have been shown to affect the TRG interpretation. On the other hand, some studies have assessed the role of molecular markers as a predictor of tumor response to neoadjuvant chemotherapy in terms of TRG. Thus, the aim of this review is to evaluate how TRG has been interpreted in gastric cancer, discuss their clinical and prognostic relevance and also address the molecular markers involved in this process.