Evaluation of histochemical methods for the detection of intracytoplasmic mucin in serous effusions

We have studied 25 serous effusions containing definitive morphologic evidence of adenocarcinoma to evaluate the ability of two mucin stains (Mayer's mucicarmine, D-PAS) to detect intracytoplasmic mucin in both cytologic (cytospin) and corresponding histological (cell block) preparations. Mucicarmine stain was positive in six of 25 (24%) cytospins and 13 of 25 (52%) cell blocks. D-PAS was positive in 19 of 25 (76%) cytospins and 20 of 25 (80%) cell blocks. Eight cases were identified which showed mucicarmine positivity in the cell block but not the corresponding cytospin; prolonging incubation time resulted in a positive mucicarmine in cytospin preparations for seven of these cases. We conclude that: (i) D-PAS is a more sensitive stain for the detection of intracytoplasmic mucin in all preparations; (ii) mucicarmine shows preferential staining for cell blocks; (iii) alterations in the staining protocol may permit mucin detection by mucicarmine staining in cytologic preparations in a significant number of cases.