Can I sue my husbands first doctor for misdiagnosing him early and since has passed away?

My husband had seen a gi doctor in Jan. He was given a colonoscopy and an mri. The doctor told him he had severe inflammation and put him on prednisone. The pain never went away. I took him to the er a month later and was told he had stage III rectal cancer. He needed emergency surgery due to blockage and was in the hospital for 20 days. The doctor he had seen told him he DID NOT have cancer and sent him home with pain meds. I had the hospital review the slides taken during the colonoscopy and his surgeon said he can not believe that no one saw the cancer as it was described as being very large. Had my husband gotten treatment sooner, he would not have needed the emergency surgery to have an ileostomy. When he saw the first doctor in Jan. he was walking and eating. When I took him to the hospital he was already in need of surgery. Since being released he had lost 60 pnds and needed to start chemo & radiation treatment. He had only 3 treatments left before he passed away April 29.