EBMT 2025 | AlloSCT in advanced systemic mastocytosis: who, when, and how?

Yeah, quite a big talk. So advanced SM is a very rare disorder. It’s a clonal abnormality of mast cells that leads to proliferation and end-organ damage in those patients with advanced disease. So it can be quite aggressive. At the moment, there is no potential cure for patients with advanced SM. So they have a poor overall survival. And in the era of tyrosine kinase inhibitors, we’ve seen very, very good responses with deep responses in the SM component, which we haven’t seen before. So most patients with advanced SM have an SM and an AHN. So it’s two hematological neoplasms in one patient, usually CMML or MPN/MDS overlap. So the whole point of transplantation and looking at that and the practice guidelines that were produced and published last year was to try and help the SM community and the transplant community to decide which was the best way to manage transplantation in these patients because there’s no single data. They’re very rare patients. So, the overview is really who do we transplant if they’ve got advanced SM and how do we manage that. In terms of who, it’s challenging but most of them have an SMHM and there are progressions of disease of up to 20% in patients even if they’ve been exposed to the new potent TKI such as avapritinib. So there’s no overall cure. And the progressions are usually in the AHN compartment, even if they’ve had very deep responses in the SM compartment. So you could go from treating the SM, AHN, SM, AHN, or you go for a cure, curative process, which is transplant, which sounds easy, but then you have to layer on the transplant issues and the outcome is affected by that. So the talk was looking at what the guidance suggested. The bottom line is those patients who have just have ASM, aggressive systemic mastocytosis or what we now call pure mast cell leukemia, they had a really poor prognosis. But if they’ve only got the cKIT mutation, they do really well with the cKIT inhibition with the new potent tyrosine kinase inhibitors. So you wouldn’t consider them for a transplant necessarily upfront. Patients with SM-AML, they are high-risk patients. You would consider them for a transplant. But there was a caveat with those that are cKIT positive, but core binding factor negative really have a very poor outlook. So, you should think about transplanting those with great caution and care. And then the patients with the SM AHN looking at both those components, deciding the prognostic risk of both those components, and then deciding when to plan for transplant. Really, the message is if you get the SM component in the best possible remission using the new TKIs or cladribine, then they have a better outcome from transplant and you also have to keep an eye on the AHN. So juggling those two to try and get them through transplant.

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