Ken-Hong Lim

TET2 mutations and their clinical correlates in polycythemia vera, essential thrombocythemia and myelofibrosis

High-throughput DNA sequence analysis was used to screen for TET2 mutations in bone marrow-derived DNA from 239 patients with BCR-ABL-negative myeloproliferative neoplasms (MPNs). Thirty-two mutations (19 frameshift, 10 nonsense, 3 missense; mostly involving exons 4 and 12) were identified for an overall mutational frequency of ∼13%. Specific diagnoses included polycythemia vera (PV; n=89), essential thrombocythemia (ET; n=57), primary myelofibrosis (PMF; n=60), post-PV MF (n=14), post-ET MF (n=7) and blast phase PV/ET/MF (n=12); the corresponding mutational frequencies were ∼16, 5, 17, 14, 14 and 17% (P=0.50). Mutant TET2 was detected in ∼17 and ∼7% of JAK2V617F-positive and -negative cases, respectively (P=0.04). However, this apparent clustering of the two mutations was accounted for by an independent association between mutant TET2 and advanced age; mutational frequency was ∼23% in patients ⩾60 years old versus ∼4% in younger patients (P<0.0001). The presence of mutant TET2 did not affect survival, leukemic transformation or thrombosis in either PV or PMF; a correlation with hemoglobin <10 g per 100 ml in PMF was noted (P=0.05). We conclude that TET2 mutations occur in both JAK2V617F-positive and -negative MPN, are more prevalent in older patients, display similar frequencies across MPN subcategories and disease stages, and hold limited prognostic relevance.

Systemic mastocytosis in 342 consecutive adults: survival studies and prognostic factors

Clinical phenotype in systemic mastocytosis (SM) is markedly variable, which complicates prognostication and decision making regarding the choice and timing of therapy. In a retrospective study of 342 consecutive adult patients with SM seen at the Mayo Clinic between 1976 and 2007, disease subdesignation according to the World Health Organization (WHO) proposal was indolent (ISM) in 159 (46%), with associated clonal hematologic non-mast cell lineage disease (SM-AHNMD) in 138 (40%), aggressive (ASM) in 41 (12%), and mast cell leukemia in 4 (1%). KITD816V was detected in bone marrow-derived DNA by allele-specific polymerase chain reaction (PCR) in 68% of 165 patients evaluated (ISM, 78%; ASM, 82%; SM-AHNMD, 60%; P = .03); JAK2V617F was detected in 4%, all in SM-AHNMD. Compared with those with nonindolent SM, life expectancy in ISM was superior and not significantly different from that of the age- and sex-matched US population. In addition, multivariable analysis identified advanced age, weight loss, anemia, thrombocytopenia, hypoalbuminemia, and excess bone marrow blasts as independent adverse prognostic factors for survival. The current study validates the prognostic relevance of the WHO subclassification of SM and provides additional information of value in terms of both risk stratification and interpretation of clinical presentation and laboratory results.

Detection of mutant TET2 in myeloid malignancies other than myeloproliferative neoplasms: CMML, MDS, MDS/MPN and AML

Detection of mutant TET2 in myeloid malignancies other than myeloproliferative neoplasms: CMML, MDS, MDS/MPN and AML

Frequent TET2 mutations in systemic mastocytosis: clinical, KITD816V and FIP1L1-PDGFRA correlates

TET2 (TET oncogene family member 2) is a candidate tumor suppressor gene located at chromosome 4q24, and was recently reported to be mutated in ∼14% of patients with JAK2V617F-positive myeloproliferative neoplasms. We used high-throughput DNA sequence analysis to screen for TET2 mutations in bone marrow-derived DNA from 48 patients with systemic mastocytosis (SM), including 42 who met the 2008 WHO (World Health Organization) diagnostic criteria for SM and 6 with FIP1L1-PDGFRA. Twelve (29%) SM, but no FIP1L1-PDGFRA patients, had TET2 mutations. A total of 17 mutations (13 frameshift, 2 nonsense and 2 missense) were documented in 2 (15%) of 13 indolent SM patients, 2 (40%) of 5 aggressive SM, and 8 (35%) of 23 SM associated with a clonal non-mast cell-lineage hematopoietic disease (P=0.52). KITD816V was detected by PCR sequencing in 50 or 20% of patients with or without TET2 mutation (P=0.05), respectively. Multivariable analysis showed a significant association between the presence of TET2 mutation and monocytosis (P=0.0003) or female sex (P=0.05). The association with monocytosis was also observed in non-indolent SM (n=29), in which the presence of mutant TET2 did not affect survival (P=0.98). We conclude that TET2 mutations are frequent in SM, segregate with KITD816V and influence phenotype without necessarily altering prognosis.

WHO subvariants of indolent mastocytosis: clinical details and prognostic evaluation in 159 consecutive adults

To the editor: The 2008 World Health Organization (WHO) proposal recognizes 2 provisional indolent systemic mastocytosis (ISM) subvariants: smoldering systemic mastocytosis (SSM) and isolated bone marrow (BM) mastocytosis (BMM).[1][1] SSM is characterized by a high burden of mast cells (MCs; [Table

Mutation in TET2 in myeloid cancers.

To the Editor: The finding of Delhommeau and colleagues that TET2 mutations occur in myeloid cancers (May 28 issue)1 has been confirmed by others.2-5 The presence of single-copy and doublecopy TET2 defects and the frequent occurrence of frameshift, nonsense, or deletion mutations are consistent with the notion that TET2 is a tumor suppressor. Delhommeau et al. suggest a role for TET2 in disease progression. We looked into this possibility by studying stored, serial bone marrow samples from eight patients with myeloproliferative neoplasms. Mutant TET2 was not detected in any of the follow-up samples, even though leukemic or fibrotic transformation occurred in three of these patients. These results are consistent with observations of similar frequencies of TET2 mutations in chronic and advanced-phase myeloproliferative neoplasms.3 We therefore believe that it is difficult to assign a specific role in the pathogenesis or progression of myeloproliferative neoplasms to mutant TET2.

Molecular analysis of secondary kinase mutations in imatinib-resistant gastrointestinal stromal tumors

Most gastrointestinal stromal tumors (GISTs) are associated with activating kinase mutation in KIT or platelet-derived growth factor receptor alpha (PDGFRA) gene, and imatinib has revolutionized the care of advanced GISTs. However, most patients gradually developed resistance to imatinib. We intend to identify the secondary kinase mutations in imatinib-resistant GISTs and to study the relationship between secondary kinase mutations and the clinical response to imatinib. Twelve advanced GIST patients, who have developed resistance to imatinib were included in this study. Paraffin-embedded pretreatment GIST specimens and progression lesions of the tumors after resistance to imatinib were analyzed for kinase mutations in exons 9, 11, 13, and 17 of KIT gene and exons of 10, 12, 14, and 18 of PDGFRA gene. Primary KIT mutations have been found in all but one of the primary tumors including one case harboring de novo double KIT exon 11 mutations. Secondary kinase mutations in KIT and PDGFRA were found in seven and 1 of 12 patients, respectively. Two patients harbored more than one secondary KIT mutations in different progression sites, and there are four types of clonal or polyclonal evolution being observed. The secondary PDGFRA exon 14 mutation H687Y is a novel mutation that has never been reported before. Acquired secondary kinase mutations are the most important cause of secondary imatinib resistance in advanced GISTs. The identification of secondary kinase mutations is important in the development of new therapeutic strategies.

KIT and Mastocytosis

KIT is a receptor tyrosine kinase that is functionally relevant for hematopoiesis, mast cell development and function, gametogenesis and melanogenesis. Normal KIT signaling requires binding to stem cell factor, and PI3K-Akt is one of the putative effector pathways. In humans, germline loss-of-function KIT mutations have been associated with piebaldism – an autosomal dominant condition characterized by depigmented patches of skin and hair. Gain-of-function KIT mutations are usually acquired and have been associated with myeloid malignancies including core binding factor acute myeloid leukemia and systemic mastocytosis (SM), germ cell tumors, gastrointestinal stromal tumors and sinonasal T cell lymphomas. KITD816V is the most prevalent KIT mutation in mast cell disease and occurs in more than 90% of the cases that fulfill the World Health Organization diagnostic criteria for SM. However, its precise pathogenetic contribution is not well understood. In clinical practice, SM is considered either indolent or aggressive depending on the respective absence or presence of symptomatic target organ dysfunction aside from skin disease. In general, conventional therapy for SM is suboptimal, and efforts are under way to develop and employ small molecule drugs that target mutant KIT.

Synthesis and evaluation of [18F]Fluorobutyl ethacrynic amide: a potential PET tracer for studying glutathione transferase.

[(18)F]Flurobutyl ethacrynic amide ([(18)F]FBuEA) was prepared from the precursor tosylate N-Boc-N-[4-(toluenesulfonyloxy)butyl]ethacrynic amide with a radiochemical yield of 3%, a specific activity of 48 GBq/μmol and radiochemical purity of 98%. Chemical conjugation of [(18)F]FBuEA with glutathione (GSH) via a self-coupling reaction and enzymatic conjugation under catalysis of glutathiontransferase alpha (GST-α) and π provided about 41% yields of radiochemical conjugated product [(18)F]FBuEA-GSH, 85% and 5-16%, respectively. The catalytic selectivity of this tracer toward GST-alpha was addressed. Positron emission tomography (PET) imaging of [(18)F]FBuEA in normal rats showed that a homogeneous pattern of radioactivity was distributed in the liver, suggesting a catalytic role of GST. By contrast, PET images of [(18)F]FBuEA in rats with thioacetamide-induced cholangiocarcinoma displayed a heterogeneous pattern of radioactive accumulation with cold spots in tumor lesions. PET imaging with [(18)F]FBuEA could be used for early diagnosis of hepatic tumor with a low GST activity as well as liver function.

Targeting epidermal growth factor receptor in lung cancer: Perspective from the Asia-Pacific region

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase of the ErbB family that is frequently overexpressed in non‐small cell lung cancer (NSCLC), and has been identified as a novel therapeutic target for lung cancer. The development of small molecule EGFR‐tyrosine kinase inhibitors (TKI) such as gefitinib and erlotinib has resulted in paradigm shift in the treatment of advanced NSCLC. The impact of EGFR‐TKI in the treatment of NSCLC is even greater in Asia–Pacific region because one of the greatest clinical benefits of EGFR‐TKI has been seen in patients of East Asian ethnicity. The discovery of somatic mutations in EGFR‐tyrosine kinase domain has so far answered some, but not all, of the questions regarding the clinical response to EGFR‐TKI in NSCLC. In addition, other molecular profiles such as KRAS mutations have also been found to play an important role in EGFR targeted therapy. In this article, we review EGFR targeted therapy in NSCLC with the focus on perspective from the Asia–Pacific region.