Genetic of multiple primary cancers

Within the frame of inherited cancer predisposition, single gene carriers of pathogenic variants (PVs) have been extensively represented in the literature, whereas the oligogenic coinheritance of heterozygous PVs in cancer-related genes is a poorly studied event. Currently, due to the increment of cancer survivors, the probability of presenting multiple primary cancers (MPC) is higher. This study included MPC patients ≤45 years without known PVs in common cancer predisposition genes. We used whole exome sequencing (WES) of germline and tumoral DNA, chromosomal microarray analysis (CMA) on germline DNA (patient 1-7, and patient 9-10), and karyotype of patient 8to detect variants associated with the disease. The ten patients included in the study presented a mean of 3 cancers per patient. CMA showed two microduplications and one microdeletion, while WES of the germline DNA identified 1-3 single nucleotide variants of potential interest to the disease in each patient and two additional copy number variants. Most of the identified variants were classified as variants of uncertain significance. The mapping of the germline variants into their pathways showed a possible additive effect of these as the cause of the cancer. Twelve somatic samples from 5 patients were available for sequencing. All the germline variants were also present in the somatic samples, while no second hits were identified in the same genes. The sequencing of patients with early cancers, family history and multiple tumors is already a standard of care. However, the growing evidence suggests that patient´s assessment should not stop at the identification of one PV in a cancer predisposition gene. A CMA identifies losses (deletion) or gains (duplication or amplification) between a tested DNA and a reference DNA which can be either the DNA of another individual or a mixture of DNA from several people. The tested DNA is labeled with a nucleotide coupled to a fluorophore (Cyanine-5-dCTP) and the reference DNA with a nucleotide coupled to another fluorophore (Cyanine-3 dCTP). These DNAs are mixed and hybridized on a microchip on which DNA fragments (oligonucleotides in the case of Agilent) corresponding to specific regions of the genome studied are deposited in specific locations. After washing the microchip, the fluorescence is measured in the emission wavelengths corresponding to the 2 fluorophores used. A fluorescence ratio is calculated at the level of each fixed DNA fragment (comparison of the patient DNA/control DNA ratio). Statistical processing of the data is then carried out using dedicated software and the result (existence of a gain or loss of a genomic segment of the patient) will be detected by a variation in the fluorescence intensity ratio beyond of a determined threshold.