Genetic medicine in companion diagnostics of germline BRCA testing of Japanese pancreatic cancer patients.

ABSTRACT

In 2021, Japan's national health insurance made germline BRCA (g.BRCA) testing available to unresectable pancreatic cancer (PC) patients as a companion diagnostic (CD) of the PARP inhibitor. This study investigated the incidence of the g.BRCA variant (g.BRCAv.) and the status of the genetic medicine associated with its testing. A total of 110 PC patients underwent the testing, five of whom (4.5%) had a deleterious g.BRCA2v. (all truncations) but no g.BRCA1v. The turnaround time (TAT) to the doctors was 13 days, and to the patients, 17 days. A higher incidence of a BRCA-related family history and a shorter TAT were seen in the g.BRCAv. patients, but they were insignificant (p = 0.085 and p = 0.059, respectively). Genetic counseling was not performed for three g.BRCA2v. patients because two of them had no accessible relatives and one died of the cancer before the genetic report was completed. Two families underwent generic counseling and testing based on the patient's genetic data. g.BRCAv. is recognized in a small fraction of PC cases, and the following genetic counseling is done more for the relatives than for the patients. TAT was constant and did not affect much on the genetic counseling, but the earlier testing is expected for patients with a deadly cancer.