MPN Workshop of the Carolinas 2025 | Hematopathology in MPNs: the WHO vs ICC classifications & applying these in clinical practice

So I’ll be speaking about the classification of myeloproliferative neoplasms, focusing on both the WHO and the ICC classification schemes. Thankfully, in the area of myeloproliferative neoplasms, there isn’t a lot of difference between the two classification systems. The approach is very much the same. There are some minor differences between the two, but it’s not, you know, it’s not a real issue like it is in MDS or AML. 

So the diagnosis is very important, right, because the care of every patient starts with a correct diagnosis; hopefully, if you don’t make an accurate diagnosis, the patient can’t get accurate care. So we take a lot of pride in making a good diagnosis for our patients with myeloproliferative neoplasms. I think, you know, in some instances today, you can argue that some patients with myeloproliferative neoplasms, like polycythemia vera, may not initially need a bone marrow biopsy, but we still do advocate for doing a bone marrow biopsy for morphologic evaluation for myeloproliferative neoplasms because sometimes you can have a patient that presents with signs and symptoms that, for all intents and purposes, look like essential thrombocythemia, but they actually have a pre-fibrotic myelofibrosis, and really, the only way to make that distinction is with doing the bone marrow biopsy. The classification systems, to go back to your original question, are really designed to capture these nuances and to make sure that we can identify these patients that are in the earlier stages of some of the more aggressive myeloproliferative neoplasms better and, you know, provide them with an accurate diagnosis that can hopefully lead to better outcomes in the future. 

Of course, I think, you know, there are always cases that haven’t read the books, and they don’t entirely fit into the classification box that we have arbitrarily created. So we do, thankfully, have a diagnostic category that is called myeloproliferative neoplasm unclassifiable. We try to reserve that really for cases that are truly unclassifiable, and, you know, we really can’t fit into one or another category, but we do leave that leeway for the pathologist because again, you don’t want to label someone with a disease that they don’t have. And so if they’re, you know, sometimes there are molecular features that overlap between several myeloproliferative neoplasms, or in the case of MDS/MPNs like CMML, they share features between myelodysplastic syndromes and myeloproliferative neoplasms, so sometimes the diagnosis is not straightforward, but we try to do the best that we can.

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