Usefulness and Limitations of Cryopreservation for Immunocytochemical Staining of Canine Cytological Specimens for Detection of Cytokeratin and Vimentin

Simple Summary Immunocytochemistry is a useful diagnostic tool in cytology; nonetheless, compared with pathological tissue specimens, cytological specimens have a crucial issue with long-term storage of antigenicity. A convenient and effective method is required for the storage of air-dried smears, which are commonly used for cytology, especially in small animal medicine. In the present study, we evaluated the usefulness of cryopreservation of air-dried smears for immunocytochemical staining for cytokeratin and vimentin, which can help distinguish between epithelial and non-epithelial tumors. The study results revealed that immunoreactivity for cytokeratin and vimentin could be detected for at least 33 months in unfixed smear samples stored in a freezer, and demonstrated the usefulness and effectiveness of cryopreserved air-dried smears in veterinary immunocytochemistry. Immunocytochemistry is an advanced diagnostic tool for identifying the origin of tumor cells. This study aimed to highlight the usefulness of cryopreserved, air-dried cytological samples in detecting cytokeratin and vimentin. Air-dried cytological smear samples were prepared from a total of 39 resected canine tumors and stored in a medical freezer without fixation. The duration of cryopreservation ranged from 2 to 56 months. The same tumors were processed for routine histopathological examination. Based on the morphological diagnosis, cryopreserved FNA smears from epithelial tumors were stained by enzymatic immunocytochemistry (ICC) for cytokeratin; those from mesenchymal and melanocytic tumors were stained by ICC for vimentin. To ascertain the positivity of tumor cells to the selected markers, tissue paraffin-embedded sections were also stained by immunohistochemistry (IHC) for the same markers. Immunoreactivity for cytokeratin was detected in cryopreserved cytological smears for a maximum of 46 months. Immunoreactivity for vimentin was clearly detected for 33 months. Smears stored at room temperature for 1 week did not show any signals under immunocytochemical examination. Thus, immunocytochemistry for cytokeratin and vimentin can be safely applied to air-dried smears cryopreserved in a freezer for at least 33 months.

Automated summary

In this study, the usefulness of cryopreserved air-dried smears for immunocytochemical staining was evaluated. The results showed that immunoreactivity for cytokeratin and vimentin could be detected for at least 33 months in the cryopreserved smears, demonstrating the usefulness and effectiveness of this method in veterinary immunocytochemistry.