Pre-Analytical Challenges during RASTesting: Tissue Quality and the Estimation ofNeoplastic Cell Percentage

Laboratories require customized feedback on improving biomarker testing practices. A workshop was organized for laboratories that participated in a European external quality assessment scheme to resolve issues related to the estimation of neoplastic cell percentage and tissue quality for RAS testing for colorectal cancer. An interactive course about tissue quality took place to stress the importance of the pre-analytical phase. During a microscopic session, five H&E stained tumor tissue slides were discussed and neoplastic cell percentages estimated. Participants included 4 pathologists, 3 molecular biologists, a technologist and a clinical geneticist from 7 laboratories. In six laboratories, tumor contents are checked routinely by visual estimation by the pathologist. The average difference between the lowest and highest estimation was 22%. During the workshop the importance of the pre-analytical phase was stressed and feedback was provided. Such initiatives can contribute in improving biomarker testing standards in Europe