Pathology-supported genetic testing for the application of breast cancer pharmacodiagnostics: family counselling, lifestyle adjustments and change of medication

Abstract

Background: Pathology-supported genetic testing (PSGT) enables transitioning of risk stratification from the study population to the individual. Research Design and Methods: We provide an overview of the translational research performed in postmenopausal breast cancer patients at increased risk of osteoporosis due to aromatase inhibitor therapy, as the indication for referral. Both tumor histopathology and blood biochemistry levels were assessed to identify actionable disease pathways using whole exome sequencing (WES). Results: The causes and consequences of inadequate vitamin D levels as a modifiable risk factor for bone loss were highlighted in 116 patients with hormone receptor-positive breast cancer. Comparison of lifestyle factors and WES data between cases with vitamin D levels at extreme upper and lower ranges identified obesity as a major discriminating factor, with the lowest levels recorded during winter. Functional polymorphisms in the vitamin D receptor gene contributed independently to therapy- related osteoporosis risk. In a patient with invasive lobular carcinoma, genetic counseling facilitated investigation of the potential modifying effect of a rare CDH1 variant co-occurring with BRCA1 c.66dup (p.Glu23ArgfsTer18). Conclusion: Validation of PSGT as a three-pronged pharmacodiagnostics tool for generation of adap- tive reports and data reinterpretation during follow-up represents a new paradigm in personalized medicine, exposing significant limitations to overcome.