Screening for the FIG-ROS1 fusion in biliary tract carcinomas by nested PCR. 
ROS1 rearrangements have been detected in a variety of tumors and are considered as suitable targets of anticancer therapies.  We developed a new, quick, specific, and sensitive PCR test to screen for the FIG-ROS1 fusion and applied it to a series of Italian patients with bile duct carcinoma (BTC).  Formalin-fixed, paraffin-embedded tissues, derived from 65 Italian BTC patients, and six cell lines were analyzed by nested PCR to investigate the prevalence of a previously reported FIG-ROS1 fusion.  The specificity and sensitivity of nested PCR were investigated in FIG-ROS1 positive U118MG cells in reconstitution experiments with peripheral blood mononuclear cells.  We found that six out of 65 (9%) BTC patients were positive for the FIG-ROS1 fusion, comprising two out of 14 (14%) gallbladder carcinoma (GBC) patients and four out of 25 (16%) extrahepatic cholangiocarcinoma (ECC) patients.  None of the 26 intrahepatic cholangiocarcinoma cases harbored the FIG-ROS1 fusion.  All the cell lines were negative for this variant.  In conclusion, 14-16% of GBC and ECC were positive for FIG-ROS1.  This may have clinical implications, since these patients will potentially benefit from the treatment with specific ROS1 inhibitors.