Evolution from heterozygous to homozygous KIT mutation in gastrointestinal stromal tumor correlates with the mechanism of mitotic nondisjunction and significant tumor progression

Abstract

Activating mutation in KIT or platelet-derived growth factor-a can lead to gastrointestinal stromal tumors (GISTs). Eighty-four cases from two institutes were analyzed. Of them, 62 (74%) harbored KIT mutations, 7 of which are previously unreported. One exhibited duplication from both intron 11 and exon 11, which has not been reported in KIT in human cancer. A homozygous/hemizygous KIT-activating mutation was found in 9 of the 62 cases (15%). We identified three GIST patients with heterozygous KIT-activating mutations at initial presentation, who later recurred with highly aggressive clinical courses. Molecular analysis at recurrence showed total dominance of homozygous (diploid) KIT-activating mutation within a short period of 6-13 months, suggesting an important role of oncogene homozygosity in tumor progression. Topoisomerase II is active in the S-and G 2 phases of cell cycle and is a direct and accurate proliferative indicator. Cellular and molecular analysis of serial tumor specimens obtained from consecutive surgeries or biopsy within the same patient revealed that these clones that acquired the homozygous KIT mutation exhibited an increased mitotic count and a striking fourfold increase in topoisomerase II proliferative index (percentage cells show positive topoisomerase II nuclear staining compared to the heterozygous counterpart within the same patient. KIT forms a homodimer as the initial step in signal transduction and this may account for the quadruple increase in proliferation. Using SNPs for allelotyping on the serial tumor specimens, we demonstrate that the mechanism of the second hit resulting in homozygous KIT-activating mutation and loss of heterozygosity is achieved by mitotic nondisjunction, contrary to the commonly reported mechanism of mitotic recombination. Keywords: homozygous KIT mutation; GIST; SNP Gastrointestinal stromal tumors (GISTs) originate from the interstitial cells of Cajal and are driven by a proliferative signal resulting from dominant activating mutations of KIT or platelet-derived growth factor receptor-a (PDGFRA).

Hereditary gastrointestinal stromal tumors sharing the KIT Exon 17 germline mutation p.Asp820Tyr develop through different cytogenetic progression pathways

“…The fact that LOH was present in the high-risk lesion is in accordance with the previously reported association of LOH with aggressive clinical behavior (O'Riain et al, 2005;Chen et al, 2008;Kleinbaum et al, 2008). Chen et al (2008) demonstrated that the mechanism of LOH in GIST is caused by mitotic nondisjunction and not by the generally accepted mechanism of mitotic recombination, in agreement with our finding of deletion of the KIT locus by FISH. Both patients here reported achieved partial response to imatinib, an ATP analogue that inhibits KIT kinase activity and blocks the phosphorylation of downstream substratum involved in the signaling transduction pathway of this receptor.…”

“…To our knowledge, this is the fifth case with hereditary GIST caused by a KIT germline mutation showing LOH in the tumor (Kim et al, 2005;O'Riain et al, 2005;Lasota and Miettinen, 2006;Kleinbaum et al, 2008). The fact that LOH was present in the high-risk lesion is in accordance with the previously reported association of LOH with aggressive clinical behavior (O'Riain et al, 2005;Chen et al, 2008;Kleinbaum et al, 2008). Chen et al (2008) demonstrated that the mechanism of LOH in GIST is caused by mitotic nondisjunction and not by the generally accepted mechanism of mitotic recombination, in agreement with our finding of deletion of the KIT locus by FISH.…”

Gastrointestinal stromal tumors: what do we know now?

“…29,[34][35][36] In serial samples from individual patients, Chen et al 36 have provided evidence that this occurs through mitotic nondysjunction, ie, failure of a chromosome 4 pair bearing the wild-type KIT allele to separate during mitosis, leaving one daughter cell with a single chromosome 4 containing the mutant KIT allele (uniparental monosomy). This correlates with increased mitotic activity and topoisomerase II expression.…”

Impact of gene dosage, loss of wild-type allele, and FLT3 ligand on Flt3-ITD–induced myeloproliferation

“…A common theme of such mutations is the acquisition of mutant allele specific imbalance (MASI) either because of copy number-neutral loss of heterozygosity or mutant allele amplification, particularly during disease progression. 1 For example, MASI affects epidermal GFR (EGFR) mutations in lung cancer and glioblastoma, 2 KIT mutations in gastrointestinal tumors, 3 and MPL mutations in myelofibrosis. 4 MASI of activated GFRs may accelerate disease through a simple gene-dosage effect, although it is also possible that loss of the wild-type (WT) protein enhances the impact of the mutant allele, for example, by enhancing formation of mutant homodimers.…”