The Quebec College of Physicians will re-read 4,500 mammograms from three clinics based on the recommendations of two medical investigators.

The expanded investigation, which began in November 2010, stems from discrepancies found in some data files during the initial investigation into quality of imaging exams at Fabreville Radiology in Laval, Quebec, and Jean-Talon Bélanger Radiology and Radiology Domus Medica clinics in Montreal.

The initial investigation into 15,000 mammograms concerned potential misreadings by one Quebec radiologist. The current review is an additional security measure and is the last stage of the investigation, the Quebec College of Physicians said in a statement.

"Currently, it is too early to conclude anything since the investigation is still open. The operation will be completed as quickly as possible and the college will release the final report as soon as possible. In total, about 22,500 films have been reviewed," said Yves Robert, MD, secretary of the Quebec College of Physicians.

All women whose studies are part of the investigation will receive a letter by mid-September, the college said.