The review covers recent research on cancer as a genetic disease manifesting both sporadically and in germline through variant genomic mutations or DNA rearrangements. This change can be point mutations, chromosomal aberrations or hypermethylation leading to DNA repair failures. Defects in tumour suppressor genes (BRCA1, BRCA2, CHEK2, PTCH1, etc.) underly hereditary predisposition to breast cancer (BC) and ovarian cancer (OC) due to genome instability. Studying somatic mutations is key to the understanding of carcinogenesis mechanisms and finding apt therapies. Heterogeneity of cancers renders the tumour mutation profiling uneasy. The treatment choice and efficacy in BC and OC depends on homologous recombination defects in tumour cells usually imposed by damaged BRCA1/2 genes. CHEK2- associated neoplasms account for most hereditary BCs linked to flaws in the DNA repair machinery. Overexpression of the PTCH1 protein is the target in breast, lung, ovarian, colonic cancers, etc.Genetic research has fundamentally altered our understanding of the aetiology and pathogenesis of human malignancy. The molecular cancer phenotype is of paramount importance in the disease prognosis and treatment personalisation.

Descripton of metastatic HER2-positive breast cancer clinical case is introduced, multilineal strategy basing on clinical situation and disease features is justified, justification of the choice of anti-HER2 treatment in every line is made, in compliance with russian and foreigh oncology associations guidelines, along with comparance of rutine treatment results and randomised trials data.