Histological assessment of tumor tissue samples via the mirror image method

Human tissue biorepositories have become key platforms for the acceleration of basic and translational biomedical research on cancer in China. The maintenance of sufficient amounts of tumor cells is critical for a wide variety of cancer studies. Ensuring the high quality of frozen stored tissue specimens is a crucial requirement. However, different tumor locations and various methods of tumor tissue removal can lead to variable numbers of tumor cells from banked tissue specimens. Thus, an effective method to assess the tumor cell content is essential for tissue samples in biobanks. In the present study, the mirror image method was used to evaluate the amount of tumor cells in stored tumor tissues of six common cancer types, including solid and hollow organ cancers. All tissues were stored in the Tianjin Medical University Cancer Institute and Hospital (TMUCIH). Histological assessment was performed by pathologists who conducted morphological diagnoses of tumor percentage on mirror image sections of frozen stored samples that were stained with hematoxylin and eosin (H&E). Results showed that the tumor percentage of solid organ cancers was higher than that of hollow organ cancers (χ(2)=17.11, p<0.0001). Among solid organ cancers, the highest tumor percentage was observed in renal tumor tissues, and likewise esophagus tumor tissues had the highest tumor content among hollow organ cancers (multiple tests, p<0.05). Three kinds of samples, which showed higher proportions of tumor content under 25%, were stomach, liver, and colorectal cancers, and the proportions were 15.0%, 10.9%, and 10.6%, respectively. Therefore, histological assessment based on the review of mirror-image H&E sections offers the most direct and objective judgment. The results can not only be applied to the tissue quality feedback process of biobanks, but also guide a wide variety of scientific studies.