The 2001 World Trade Center (WTC) attack exposed workers to known and suspected carcinogens. Studies have identified a risk of some cancers in responders compared to the general population. We studied latency and persistence of risk in were 16,221 exposed participants using piecewise exponential survival models to estimate rate ratios and associated 95% confidence intervals; change points in the rate ratios were estimated using profile likelihood. We observed 388 incident prostate and 47 colon cancer cases. Prostate cancer rates were mildly elevated between 2002 and 2008 (RR=1.41, 95%CI 1.16-1.71), significantly elevated between 2008 and 2012 (RR=1.94, 95%CI 1.68-2.24), and diminished between 2012 and 2015 (RR=1.29, 95%CI 1.07-1.57). Colon cancer was not associated with WTC exposure. While the exposures at the WTC site are a plausible culprit for the observed effect, screening practices (PSA) in this monitoring program cannot be discounted.