Fragile sites of chromosomes are represented by parts of DNA with tandem repeated di- or trinucleotide replications forming unusual DNA structures; such expansions of nucleotide replications are observed in the regions of expression genes and cause dynamic mutations. Specific fragility of chromosomes in the spectrum of rare sites is frequently revealed in patients with hereditary forms of cancer. While studying chromosomes of the peripheral blood lymphocytes in patients with cancer of the endometrium there were found 22 fragile sites, 19 of them coincide with the known sites of fragility, 3 fragile sites are unknown so far (1p1.2; 12q1.1; 18q1.1).
