Study of Ret Ploidy in Mtc: In Silico Analysis and Mlpa (Multiple Ligation–Dependent Probe Amplification) Validation

  • Background: Medullary Thyroid Carcinoma (MTC) is related to RET proto-oncogene alterations: germline RET mutations are present in about 98% of hereditary cases and somatic mutations in 50-75% of sporadic cases. MTC is also associated with chromosome 10 amplification or loss.

    Purpose: Aim of the study was to evaluate the RET copy number variation (CNV) and to correlate CNV with mutation profile.

    Materials and Methods: 175 sporadic cases, previously characterized with a NGS approach, have been reanalyzed with the ION Reporter software to reveal CNVs. In 29 cases RET CNV have been verified by MLPA.  These data have been correlated with the mutation profile and with RET mRNA expression.

    Results: Seven cases (3.7%) were aploid (CNV?1.5), 128 (72%) were diploid (1.5<CNV?2.4) and 43 (24.3%) showed a RET amplification (CNV?2.4). In silico data have been confirmed by MLPA in 23/29 cases (79.3%). We demonstrated that the prevalence of RET CNV altered cases (deleted or amplified) was higher in RET (36/99, 36.4%) and RAS (10/43, 23%) positive cases while, in not mutated cases, the majority of tumors were diploid (30/33, 91%). No difference was found when analyzing different RET mutations. No correlation was found between CNV and RET expression levels.

    Conclusions: We demonstrated that MTC is mainly diploid but aneuploidy can occur in a high percentage of cases. In addition RET CNV are associated with RET and RAS mutations. The question of whether CNV is a late phenomenon in tumor development/progression or if it is a causative event remains to be proved.

 

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