dysplasia

Can long term use of asacol (on & off for 20 years) have  any bearing on the results of a biopsy?  With a history of UC should I trust my doctor's prognosis to have my colon removed as a prevention to cancer?  I am wondering if there has been any studies on whether the use of asacol can cause dysplastic cell changes or do I trust that it is the disease which as been inactive.  If I went off the asacol would I increase or speed up the dysplasia ( I understand the colitis may flare up) or would I get a truer reading say in a couple of months with another colonoscopy.