[Authorization of pathologists for the estimation of the tumor cell percentage on tissue sample for molecular analysis purpose].

Before molecular analysis is performed, morphological control with an estimation of the tumour cell percentage (%TC) could have a major impact on mutation detection. Accreditation according to NF EN ISO 15189 commands an authorization through evaluation of skills. The objective of this work was to validate the empowerment of pathologists to estimate %TC in tissue sample prior to molecular analysis. The accreditation technical guidance methods in Medical biology and histopathology were taken as references. %TC was the ratio of tumour cell nuclei on all nuclei within the area selected for the DNA extraction. External evaluations quality scores were used for accuracy. In order to assess the intermediate precision, 35 %TC estimation were performed 15 days apart in 4 samples (biopsies, transparietal biopsies or surgical specimen, either fixed or frozen) by 7 pathologists. Three other cases with interference (inflammation, mucus, necrosis) were evaluated. A result was satisfactory if %TC were within ±20 % of expected percentage obtained by the average of 35 estimates. The performances were satisfactory since no estimate was made more than 20 % of the expected percentage. Low interpathologists reproducibility has been reported in the literature and can have a consequence on molecular analysis in samples with low %TC, where the value reach the analytical sensitivity thresholds of molecular techniques. The current report is an example of a step of the accreditation process, which is a challenge for pathologists' activity in the future.