Unique mutational profile associated with a loss of TDG expression in the rectal cancer of a patient with a constitutional PMS2 deficiency.

Cells with DNA repair defects have increased genomic instability and are more likely to acquire secondary mutations that bring about cellular transformation. We describe the frequency and spectrum of somatic mutations involving several tumor suppressor genes in the rectal carcinoma of a 13-year-old girl harboring biallelic, germline mutations in the DNA mismatch repair gene PMS2. Apart from microsatellite instability, the tumor DNA contained a number of C:G→T:A or G:C→A:T transitions in CpG dinucleotides, which often result through spontaneous deamination of cytosine or 5-methylcytosine. Four DNA glycosylases, UNG2, SMUG1, MBD4 and TDG, are involved in the repair of these deamination events. We identified a heterozygous missense mutation in TDG, which was associated with TDG protein loss in the tumor. The CpGs mutated in this patient's tumor are generally methylated in normal colonic mucosa. Thus, it is highly likely that loss of TDG contributed to the supermutator phenotype and that most of the point mutations were caused by deamination of 5-methylcytosine to thymine, which remained uncorrected owing to the TDG deficiency. This case provides the first in vivo evidence of the key role of TDG in protecting the human genome against the deleterious effects of 5-methylcytosine deamination.

[Gastrointestinal stromal tumor molecular diagnostics in relation to the prediction of a therapeutic response to targeted biological therapy]. / Molekulární diagnostika gastrointestinálních stromálních tumoru ve vztahu k predikci terapeutické odpovedi na cílenou biologickou lécbu.

Targeted therapy based on the inhibition of the receptor tyrosine kinases has improved the outcome of patients with metastatic, recurrent and/or unresectable gastrointestinal stromal tumors (GIST). Activating mutations of KITand PDGFRA genes, which code for receptor tyrosine kinases, play an important role in the malignant transformation of stromal cells in the gastrointestinal tract. The response to targeted therapy is associated with the presence and type of mutations. Molecular identification of the primary mutational status became an important tool in predicting the response to therapy (sensibility/resistance). The identification of secondary mutations occurring in patients treated with targeted therapy may explain the cause of acquired, secondary resistance of GIST. In these cases, mutational analysis represents a tool to explain failure of the therapy and provides a rationale for alternative therapeutic strategies.

Rhabdomyosarcoma: molecular analysis of Igf2, MyoD1 and Myogenin expression.

Rhabdomyosarcoma is the most common soft tissue sarcoma of childhood. There are two major histopathological types of RMS ­ embryonal (eRMS) and alveolar (aRMS). A molecular study of Igf2, MyoD1 and Myogenin was performed to determine the expression profiles and to assess the possible utility of these genes as potential treatment targets. Patients with RMS showed up to 100-fold increase of Igf2 transcription in comparison with normal skeletal muscle. Our data suggest that overexpression of Igf2 occurs in RMS of both histological subtypes. No correlation between the results of Igf2 mRNA expression and LOH at the 11p15 region (p= 0.12) was observed, but there was a trend of a higher expression of Igf2 mRNA in RMS samples with LOH. We observed a high level of MyoD1 mRNA in both aRMS and eRMS, and we detected a similar level of MyoD1 mRNA in RMS and normal skeletal muscles. There was a correlation between the results of MyoD1 mRNA expression and LOH at the 11p15 region.We did not observe any statistical difference in the level of Myogenin mRNA in the subgroups of RMS. Analogous to MyoD1, we observed a similar level of Myogenin mRNA in RMS and normal skeletal muscles.