MedicalResearch.com Interview with:
Jason R. Gotlib, MD
The Clinical Investigator Pathway
Hematology Division
Stanford University Medical Center
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: The background is that advanced forms of systemic mastocytosis, which are blood cancers characterized by accumulation of abnormal mast cells in the bone marrow and additional organs, represent a group of orphan diseases with a large unmet need. Approximately 90% of patients harbor the acquired KIT D816V mutation, a mutated receptor tyrosine kinase on the surface of mast cells which a primary driver of disease pathogenesis. Only 1 drug is approved for patients with one form of advanced systemic mastocytosis, termed ‘aggressive systemic mastocytosis, or ‘ASM’. This therapy is imatinib (Gleevec), but it is only approved for patients without the KIT D816V mutation, or with KIT mutation status unknown because the KIT D816V mutation is resistant to imatinib. Therefore, this drug may only be useful for approximately 10% of patients. Other drugs that have been used off-label for systemic mastocytosis (but are not approved for this indication) include interferon-alpha or cladribine, which show some activity, but their evaluation to date has been primarily limited to small case series which are usually retrospective in nature, and include mixed populations of systemic mastocytosis patients who have both early stage disease without organ damage (e.g. indolent systemic mastocytosis) and and advanced stage patients, as included in this trial, who have one or more findings of organ damage. Also, those trials employed differing response criteria and no central adjudication of eligibility and response assessments was undertaken.
Midostaurin is a multikinase inhibitor with activity against both wild-type KIT, but most importantly, KIT D816V (in contrast to imatinib). Prior work demonstrated that cell lines transformed with the KIT D816V mutation can be inhibited at relatively low concentrations of midostaurin. These concentrations could also be achieved in vivo (e.g. at concentrations achievable in the blood of patients). Cell lines transformed by KIT D816V could not be inhibited by imatinib.
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