Usefulness and limitations of cryopreservation for immunocytochemical staining of cytological specimens

Immunocytochemistry is an advanced diagnostic tool used to identify the origin of tumor cells. The present study aimed to clarify the usefulness of cryopreserved, air-dried cytology samples for the detection of cytokeratin and vimentin. Air-dried smear samples were prepared from canine tumors and stored at –30°C or room temperature without fixation. The duration of cryopreservation varied from 2 months to 4 years and 8 months. Formalin-fixed paraffin sections were also prepared from these tumors. These samples underwent enzymatic immunocytochemistry and immunohistochemistry for the detection of cytokeratin and vimentin. Immunoreactivity for cytokeratin was detected in samples cryopreserved for a maximum of 3 years and 10 months. Immunosignals for vimentin were clearly detected for 2 years. Expression of cytokeratin and vimentin was not detected in samples stored at room temperature for 1 week. Immunoreactivity was observed in all specimens using immunohistochemistry. These findings suggest that immunocytochemistry for cytokeratin and vimentin can be safely applied to air-dried smears that have been cryopreserved at –30°C for at least 2 years. This simple method may be useful for retrospective cytological studies and/or re-evaluation of cytology results.