PKC412 (Midostaurin) Is Safe and Highly Effective in Systemic Mastocytosis Patients: The Bologna Experience
Authors: Papayannidis Cristina , Abbenante Mariachiara , Parisi Sarah , Paolini Stefania , Iacobucci Ilaria , Frabetti Federica , Ottaviani Emanuela , Ferrari Anna , Guadagnuolo Viviana , Sartor Chiara , Soverini Simona , De Benedittis Caterina , Baldazzi Carmen , Testoni Nicoletta , Baccarani Michele , Martinelli Giovanni 
Published: October 2019

Abstract
Abstract 1749

Introduction.
Mastocytosis is a myeloid neoplasm characterized by abnormal accumulation and frequent activation of mast cells (MCs) in various organs, mostly bone marrow, skin, liver and gastrointestinal tract. In most adult patients, the systemic form of mastocytosis (SM) is diagnosed, which includes an indolent, an aggressive and a leukemic subvariant. The c-kit mutation D816V is detectable in most adult patients with SM. Treatment of SM usually focuses on symptom relief by histamine receptor antagonists and other supportive therapy. However, in aggressive and leukemic variants, cytoreductive and targeted drugs must be applied.

Methods.
From 2008, 11 patients (male/female=3/8) affected by Mastocytosis, have been referred to our Institution. The median age was 53 years. All the patients underwent a bone marrow biopsy, with flow citometry and molecular biology analysis, in order to identify the presence of D816V mutation of c-Kit gene. Serum tryptase level was tested, resulting elevated in all cases. According to 2008 WHO diagnostic criteria, 9 patients presented with SM, whereas in the other cases a skin isolated involvement was detected. Systemic symptoms were characterized by nausea, diarrhoea, asthenia, weight loss, pruritus and serotine fever, identifying an aggressive form of the disease in 5/11 patients, due to skeletal involvement in three cases, ascitis and liver function impairment in another one and bone marrow disfunction in the fifth one. Therefore, since a first line therapy with supportive care and histamine receptor antagonists wasn't followed by a significant benefit, a personalized use of PKC412 was asked and obtained for all these five patients.

Results.
From March 2011 three out of the five patients with aggressive SM have received a prolonged period of treatment with PKC412, which was administered orally, at the dosage of 100 mg twice daily, without rest periods. The drug was well tolerated. No serious adverse events were observed. All the patients obtained a quick and prolonged improvement of clinical symptoms, in terms of weight gain, bowel function and skeletal pain. At the bone marrow evaluation, the persistence of the D816V c-kit mutation was observed, despite a significant decrease of mast cell marrow involvement. In one case we observed, after a first good response, a disease progression, characterized by the sudden reoccurrence of the same symptoms detected at diagnosis, confirmed by a relevant expansion of a pathologic mast cell population in the bone marrow. After a rest period, the drug was readministered, and a second remission was obtained.

Conclusions.
PKC412 is safe and effective in patients with SM, being able to significantly improve not only the gastrointestinal and systemic symptoms, but also the haematological profile. The persistence of the D816V c-kit mutation, despite a morphologic remission, suggests that many other oncogenic factors may be responsible for the pathogenesis of the disease.

Acknowledgments.
Work supported by European LeukemiaNet, AIRC, AIL, PRIN, Fondazione del Monte di Bologna e Ravenna, University of Bologna.

Disclosures:
Baccarani: Novartis: Consultancy, Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau; PFIZER: Consultancy, Honoraria, Speakers Bureau; ARIAD: Consultancy, Honoraria, Speakers Bureau. Martinelli:NOVARTIS: Consultancy, Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau; PFIZER: Consultancy; ARIAD: Consultancy.