[Pathogenic large duplication in TP53 as a hereditary predisposing factor in breast cancer]

Germline pathogenic variants of TP53 are associated with Li-Fraumeni syndrome and represent a high risk for hereditary breast and ovarian cancer. We identified a germline, multi-exon heterozygous duplication variant in TP53, NM_000546.6:dup(ex2-5), in a young triple-negative breast cancer patient. We aimed to assign its pathogenicity.

DNA and RNA (cDNA) level specific amplification tests and sequencings were performed to identify the genomic duplication breakpoint and to detect the presence of defective transcripts.

cDNA tests revealed aberrant transcript, which causes a shift in the reading frame. Allelic imbalance was also observed, indicating degradation of the defective RNA product. By locating the breakpoints at the DNA level, we determined that 6975 bp was repeated in tandem and in the same orientation. We also revealed the possible mechanism of the structural rearrangement.

We established that the duplication identified at DNA level manifested in the mRNA and coded for a non-functional protein. Based on these data, we were able to classify this duplication variant as pathogenic, which affects the patient's therapeutic options and justifies genetic screening of family members.