Quality of cell blocks prepared from residual pleural effusion and bronchial washing samples for immunocytochemistry

Cell blocks (CBs) enable the long-term preservation of cytological samples. The aim of this study was to analyse the quality of CBs prepared from leftover fluid from lung adenocarcinoma pleural effusion samples and residual bronchial washing sediment for immunocytochemistry.

The residual part of 455 lung adenocarcinoma pleural effusion samples and sediment from 384 bronchial washing samples were used to prepare CBs following the agarose method. The quality of CBs was evaluated based on the quantity of malignant cells in haematoxylin and eosin-stained slides and interpreted as optimal or insufficient for immunocytochemistry. Immunocytochemistry on CBs was performed using the Dako EnVision™ FLEX detection visualisation system. The CB results for TTF-1, ALK, and PD-L1 immunocytochemistry were compared with the corresponding cytological smears.

Among all CBs, 202 (44.4%) from leftover pleural effusion fluid and 85 (22.1%) from residual bronchial washing sediment had an optimal number of lung adenocarcinoma cells. Eight pleural effusion CBs were stained for TTF-1. Four pleural effusion and two bronchial washing CBs were stained for ALK and PD-L1. All tested pleural effusion CBs were confirmed positive for TTF-1 and negative for ALK. The PD-L1 tumour proportion score (TPS) was ≥ 50% in two pleural effusions. ALK was confirmed negative in bronchial washing CBs. One bronchial washing CB was interpreted as PD-L1-negative while the corresponding smear was positive (TPS ≥1%; 2%).

The CB results of TTF-1, ALK, and PD-L1 corresponded to the findings for the smears. The inclusion of CBs prepared from leftover fluid from pleural effusion samples and residual bronchial washing sediment in routine cytological practice could provide a source of high-quality material for immunocytochemistry in addition to smears and cytospins.