Opdivo, GI bleeding, ulcers, hemorrhoids ?

In July 2017 my dad was diagnosed with stage 3c melanoma. He had an 8mm ulcerated tumor on head and 4mm in one lymph node (didn’t do complete dissections.) In September he went on one year of Opdivo. He had a rash, fatigue joint pains and was slightly anemic but otherwise tolerated everything well.. A few months after his final opdivo around December/January he discovered blood in the stool and was hospitalized with severe anemia and received a blood transfusion. They did an endoscopy, colonoscopy and pill camera. They didn’t find any tumors but two small benign non-bleeding ulcers in the stomach and hemorrhoids. The bleeding in the stool continued and he continued getting iron infusions and blood transfusions every two weeks (has had about ten of each now.) In April they did a hemorhoidectomy (also negative test for malignancy), which reduced the pain of the hemorrhoid, but two months later he is still has blood in the stool and needs the blood/iron transfusions. We are not sure if the hemorrhoid isn’t healing or if there is some other problem in the GI track. Earlier this week they did a GI scan (nuclear test where red blood cells are tagged and photographed.) but the result came back as not showing any internal bleeding over a two hour period.

I was wondering if anyone else had a similar experience? And if so, what did you do? I haven’t really come across hemorrhoids or stomach ulcers as symptom of opdivo although see a lot on colitis (which the doctors say he doesn’t have.)

Thank you