Outsourcing cytological samples to a referral laboratory for EGFR testing in non-small cell lung cancer: does theory meet practice?

Objective: Guidelines from the College of American Pathologists (CAP), the International Association for the Study of Lung Cancer (IASLC) and the Association for Molecular Pathology (AMP) consider cytology suitable for testing epidermal growth factor receptor (EGFR) mutations in lung adenocarcinoma. The guidelines recommend that cytopathologists first discuss the possibility of testing squamous cell carcinomas (SqCC) in multidisciplinary meetings. Second, cell blocks should be analysed rather than smear preparations and, third, specimens should be sent to external molecular laboratories within three working days of receiving requests. This study monitored how these recommendations are met in practice.

Methods: Our laboratory received 596 requests from cytologists from 13 different institutions. For each case, the cytological diagnosis, cytopreparation type, and time between the request and sample mailing were compared with the recommendations.

Results: Of the 596 samples, 32 (5.4%) had been reported as SqCC. Three of these (9.4%) showed EGFR mutation. Cytological slides, either ThinPrep(™) (51.2%) or direct smears (43.2%), were more frequently received than cell blocks (5.7%). The mean time between the oncologist's request and specimen dispatching was 5.8 working days.

Conclusions: The occurrence of mutations in samples reported as SqCC was higher than expected. This questions the reliability of the original diagnosis, which reinforced the recommendation to evaluate the opportunity for testing non-adenocarcinoma cytology on a case-by-case basis. In spite of CAP/IASLC/AMP recommendations, cell blocks were underutilized for EGFR testing, but cytological slides were suitable for DNA analyses. Significant efforts are needed to avoid delays in outsourcing cytological samples for EGFR testing.