Pathologic response to preoperative therapy: Does it mean what we think it means?

Tumors treated with preoperative chemotherapy or radiation often demonstrate evidence of response in the resection specimen. Pathologic response is often interpreted as a surrogate for recurrence or survival outcomes. With a valid surrogate for long-term outcomes, investigators can explore treatment strategies with immediate endpoints. The financial and time costs of trials measuring recurrence and survival may be lessened by using short-term pathologic outcomes as an endpoint. This review is intended to examine the current status of pathologic response as a surrogate for tumor behavior. We address questions regarding the definitions of pathologic response, as well as the current literature regarding the meaning of pathologic response for some common tumor types. We explore some of the potential confounding effects that may explain the frequent discordance between tumor response and patient outcomes. In addition, we address some alternative strategies to gauge the response of a tumor to preoperative therapy.