The Université de Nantes' Céline Bossard and colleagues discuss KRAS mosaicism in metastatic colorectal adenocarcinomas in the Journal of Clinical Pathology. The researchers examined 18 patients with metastatic colorectal cancer and determined the mutational status of their tumors — including primary tumors, synchronous and metachronous metastases, and a recurrence — through PCR and direct sequencing. Bossard et al. report that KRAS mutational status agreed between primary tumors and matched metastases for 14 of the 18 patients, though it did not agree in four. "In some patients, we were able to detect a KRAS mutation in the primary tumor but not in matched metastases, and a KRAS mutation in some metastases but not in others. These findings can be explained by the successive and/or parallel clonal expansions at intermediate stages during the multistep evolution of the tumor," the researchers write.

In an opinion article, the University of Western Australia's David Ravine and the University of Adelaide's Graeme Suthers say there is not enough information regarding the risk of preanalytical errors in genetic testing. "Like the proverbial elephant in the room, we know the errors are present but we hesitate to talk about them. The issue must be addressed, however, because errors in genetic testing have the potential to prompt clinical decisions with a high risk of attendant harm," Ravine and Suthers write.