Hi Steve,
Let me preface by saying that I am not a doctor just a bone marrow failure patient with 5.5 years of experience
It seems like the immunohistochemistry is just listing possible reasons why those markers would be expressed. I use to just get my markers with no explanations. So that was why I was concerned about the GI stoma notation.
Based on the rest of the report, it could be MDS or it could be something else. The traditional "smoking guns" are cytogenetic abnormalities, blasts, or significant dysplasia. He does have dysplasia in his platelet line, but he also doesn't have a lot of platelet precursors (megakaryocytes). So to me, it is not obvious.
I would seek out that third opinion from an MDS Center of Excellence. Also, keep aggressively pursing a switch in the medicines.