The length of time from the date of diagnosis or the start of treatment for a disease until the disease starts to get worse or spread to other parts of the body. In a clinical trial, measuring the time to progression is one way to see how well a new treatment works. Also called TTP.

Assessment of [[perfusion]] in early post-treatment MR imaging can stratify TTP in patients with glioblastoma for adjuvant [[temozolomide]] therapy. Positive perfusion in surgical cavity wall enhancement (SCWE) can become a predictor of a longer TTP.