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Human tryptase is a serine protease expressed in mast-cells. We previously observed that AML blast cells, cultured in vitro from a KIT D816Y patient, give rise to adherent cells with mast-cell like phenotype and tryptase was released in the serum-free medium. To correlate total serum tryptase (ts-try) levels with cytogenetic features and KIT mutational status, we analyzed serum samples from AML patients at diagnosis. In 70 out of 155 patients (45%) we detected elevated ts-try (>15 ng/mL), significantly linked to t(8;21) (P < .001) and inv(16) (P = .007). In patients that achieved complete remission the ts-try decreased to normal values. In 75 patients screened for KIT mutation, we found a clear relationship between elevated ts-try and mutated patients with t(8;21) (P < .001). In conclusion, we propose that checking for ts-try at diagnosis of AML may be a simple tool to select patients to be addressed to KIT mutation screening.

Background: Mutations involving KIT and FLT3 genes, encoding tyrosine kinase (TK) membrane receptors, are detected in core-binding factor leukaemia (CBFL) patients. PDFGRA and PDGFRB encode class III TK receptors and are involved both in physiological processes and in the pathogenesis of haematological and solid tumours. The aim of this study was to investigate if PDGFR mutations are involved in CBFL., Patients and Methods: In order to detect PDGFR mutations in CBFL, 35 patients without KIT or FLT3 mutations patients were screened by rapid and sensitive single-strand conformation polymorphism (SSCP) analysis. Sequence analysis was performed in polymerase chain reaction (PCR) products showing altered mobility in SSCP analysis in order to determine the nucleotide changes., Results: Three types of single-nucleotide polymorphism (SNP) were detected in the PDGFRA gene (exon 12, exon 13 and exon 18) while no mutation of PDGFRB was detected in the tested CBFLs., Conclusion: These data showed that no pathogenic mutations in PDGFRA and PDGFRB were detected in the context of CBFL without KIT and FLT3 mutations. Thus, PDGFR genes do not seem to be involved in CBFL and future studies are needed to establish the genetic causes of the disease in these particular patients.

Distinct forms of tyrosine kinase domain (TKD), juxtamembrane domain, exon 8, and internal tandem duplication (ITD) mutations of c-KIT, were observed in about 46% of core binding factor leukemia (CBFL) patients. To evaluate their prognostic significance, 67 adult patients with CBFL were analyzed to ascertain the c-KIT mutation status. In acute myeloid leukemia (AML) with t(8;21), the presence of c-KIT TKD mutation at codon 816 (TKD(816)) was associated with a high white blood cell count at diagnosis (median, 29.60 x 10(9)/L) and a higher incidence (33%) of extramedullary leukemia (EML) during the course of the disease. Data also showed that the TKD(816) mutated patients (n = 12) had a significantly higher incidence of relapse and a lower overall survival (OS) at 24 months, compared with the 17 c-KIT unmutated (c-KIT(-)) patients (90% vs 35.3%, P = .002; 25% vs 76.5%, P = .006, respectively). No difference in relapse incidence (P = .126) and OS (P = .474) was observed between the c-KIT mutated other than TKD(816) (n = 7) and the c-KIT(-) patients. These findings indicate that c-KIT TKD(816) mutation has a negative impact on the outcome of AML with t(8;21).

Aim of this study is to investigate the capability of Imatinib to induce an anti-leukemic effect in Core Binding Factor (CBF)-leukemia patients presenting either with extracellular juxtamembrane or kinase KIT mutations. On the basis of a screening analysis for KIT mutations, two patients with a kinase mutation and one with extracellular juxtamembrane mutation, in first or subsequent leukemic relapse, received 400mg Imatinib twice daily for 30 days. After Imatinib discontinuation, bone marrow cells were re-tested to assess the KIT mutational status and the chromosomal set. In our experience, none of the treated patients had a response by standard criteria; in particular, we did not observe any activity against acute myeloid leukemia (AML) associated with KIT kinase mutations. However, in the patient with extracellular juxtamembrane mutation, Imatinib seems to have some clinical beneficial effect and, most important, is able to abrogate the leukemic subclone carrying the mutation. Whether Imatinib, in combination with other agents, may play a role in the treatment of AML with more sensitive extracellular juxtamembrane KIT mutation remains to be determined.

Background and Objectives: Mutations of KIT receptor tyrosine kinase are involved in the constitutive activation and development of human hematologic malignancies. Gain-of-function mutations in the second intracellular kinase domain (TK2) and in the juxtamembrane domain are described in patients with core binding factor acute myeloid leukemia (CBFL) and are associated with leukocytosis. We evaluated the incidence of KIT mutation in 52 adult patients with de novo CBFL and in 49 FLT3/ITD-negative childhood patients with de novo acute myeloid leukemia (AML), excluding cases of acute promyelocytic leukemia., Design and Methods: In order to analyze the role of KIT in CBFL we examined the KIT mutations in 52 adult CBFL, including 15 previously reported patients, and in 49 non-APL childhood AML patients using sensitive detection methods. We correlated our findings with the presence of trisomy 4 and investigated the relationship of the extra chromosome 4 with KIT mutations., Results: Several kinds of gain-of-function KIT mutations were found in 24 of the 52 (46.1%) adult CBFL cases and 6 of the 49 (12.2%) non-APL childhood AML patients. KIT mutations were detected in 4 of the 8 adult patients and one childhood AML case bearing trisomy of chromosome 4 as either the sole cytogenetic aberration or a karyotypic aberration additional to t(8;21). In three of the trisomy 4 cases we demonstrated that trisomy 4 leads to duplication of the KIT mutated allele., Interpretation and Conclusions: These results underline that the KIT gene is activated in AML characterized by distinct cytogenetic and molecular genetic patterns and represents the most frequently mutated target in adult CBFL.

Mutations of the c-kit gene have been reported in myeloproliferative disorders. We describe here a case of Ph+ (b2a2) chronic myelogenous leukemia that, during the course of disease, showed an unusual bone marrow mast-cell infiltration. A mutational screening for the c-kit gene, performed on DNA routinely cryopreserved during the follow-up, evidenced the D816Y-activating mutation as an additional genetic abnormality. Treatment with imatinib mesylate resulted in a substantial decrease of the BCR-ABL/ABL ratio and in the absence of c-kit mutation. It is likely that the superimposed c-kit mutation, in this case, may account for the transient bone marrow mastocytosis.