Intraperitoneal free cancer cells in non‐gynaecological adenocarcinomas: a reproducibility study

E. Piaton, L. Villeneuve, C. Maurice, C. Paulin, M. Cottier, B. Fontanière, M. Salle, D. Seigneurin, S. Vancina, E. Decullier, F. N. Gilly and E. Cotte Intraperitoneal free cancer cells in non‐gynaecological adenocarcinomas: a reproducibility study Objective: In recent years, therapeutic approaches including cytoreductive surgery followed by intraperitoneal chemotherapy have proven effective in peritoneal carcinomatosis of colorectal origin. If cytology is to be used to include patients in aggressive treatment regimens, it is necessary to evaluate its performance, particularly in terms of specificity. The aim of this study was to assess interobserver agreement for the detection of intraperitoneal free cancer cells (IFCCs) in patients with non‐gynaecological adenocarcinomas. Methods: Over a 5‐year period, 1223 patients were recruited in 19 French surgery departments. Peritoneal samples were examined in 14 dispersed pathology laboratories. Giemsa‐stained slides were sent to a control reader blind to the previous diagnosis. Discordant cases, concordant positive results and a random selection of negative concordant cases were reviewed by a panel of seven cytopathologists. The ‘final diagnosis’ was that of the consensus meetings but took into account locally‐processed slides. Results: Gathering dubious cases with negative results, a 95.6% concordance was achieved between local readers and the control reader. IFCCs were ascertained by the panel in 85 cases (7.0%). Eight of 873 colorectal cancers cases viewed locally were falsely positive (0.9%). Radiotherapy and neoadjuvant therapy had no impact on the false‐positive rate as assessed by final validation by the panel (P > 0.05). Samples initially considered as dubious were reclassified as negative by the panel in 24 of 25 cases (96.0%). Conclusions: The panel consensus allowed reclassification of most dubious/equivocal peritoneal cytology cases, whereas clearcut distinction between benign and malignant cases was correctly achieved in almost all cases.