Appellants made out a prima facie case by establishing that they did not commit medical malpractice in their treatment of plaintiff. The burden then shifted to plaintiff to adduce admissible proof raising a triable issue of fact. However, plaintiff's expert offered only conclusory assertions and mere speculation that her cancer would have been discovered earlier and would not have spread if appellants had more aggressively pursued her, and expedited and tracked her follow-up visits more actively ( see Alvarez v. Prospect Hosp., 68 NY2d 320, 325; Bullard v. St. Barnabas Hosp., 27 AD3d 206; DeFilippo v. New York Downtown Hosp., 10 AD3d 521, 523). Furthermore, in concluding that plaintiff's cancer should have been discovered by December 1998, plaintiff's expert improperly relied on information which could not have been known to plaintiff's doctors during the time they treated her ( see Lederman v. Lawrence Hosp., 202 AD2d 198, 199-200).