Former President Joe Biden‘s announcement Sunday that he has an aggressive form of prostate cancer has led to questions about how something so serious could have been missed or whether he received the appropriate treatment. Critics, meanwhile, have alleged a cover-up after doctors said he likely has had the disease for years.

Biden announced he was diagnosed with prostate cancer with a Gleason score of nine and in Grade Group 5, the highest grade group of abnormality, according to the American Cancer Society. On Monday, he commented on his diagnosis, thanking people for their support.