[Clinical Cancer Genetics: A guide for the pathologist]

It is paramount to identify patients whose cancer is associated with genetic susceptibility to the disease, since their long-term management depends on it. Anatomical and molecular pathologists play a key role in the process. Indeed, their diagnosis supports or even sometimes warrants germline genetic testing. For example, a colorectal cancer with mismatch repair protein expression loss suggests Lynch syndrome, while a rare type of renal cell carcinoma with fumarate hydrate expression loss is highly evocative of hereditary leiomyomatosis and renal cell carcinoma syndrome. Similarly, the presence of the T790M EGFR variant before treatment in a non-small-cell lung carcinoma warrants further testing as the variant is likely of germline origin. Patients with suspected genetic susceptibility to cancer are referred to the nearest clinical cancer genetics clinic. The cancer geneticist, assisted by a genetic counsellor, then collects detailed personal and familial information, sometimes feeds them into bioinformatics tools or clinico-pathological scores, decides whether germline genetic analysis is justified, determines which genes should be analysed and prescribes testing. Germline testing is carried out on a blood sample by expert laboratories using next generation sequencing on panels of cancer susceptibility genes. The cancer geneticists then return the result to the patient. When a pathogenic variant is identified, the patient's management is modified, with recommendations ranging from intensified surveillance to risk-reducing surgery. Treatment is sometimes adapted to the pathogenic variant. In addition, relatives can undergo genetic testing, should they wish to know whether they carry the familial variant. In the near future, we expect clinical cancer genetics to move towards strengthened partnerships with molecular pathologists and medical oncologists. Somatic genetic analyses are now routine, at least in metastatic cancer, and a proportion of the tumoral variants identified are actually of germline origin. As for the oncologists, the development of mainstreaming programs where they are allowed to prescribe germline testing under the supervision of a cancer genetics team is unavoidable.