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Molecular and pathological evaluation of cryopreserved colorectal cancerous tissues: Effects of freezing method and cryoprotection.

BACKGROUND
Snap freezing and RNAlater stabilization are methods that were wildly used in biospecimen depositories to preserve cancer tissues. Both methods have its own limitations. An ideal method for preservation of diseased tissues should permit the broader uses of stored tissue samples, including not just for molecular diagnostic analysis, histopathological evaluation, but also for the recovery of functional live cells and tissues as well as the regeneration of patient-derived xenograft (PDX) models for the drug screening study.


MATERIALS AND METHODS
This study investigated molecular and pathological evaluation of cryopreserved colorectal cancer tissues, with an emphasis on effects of freezing method and cryoprotection. Global gene expression analysis with microarrays and histological examination of tissue samples were performed to compare tissue specimens after snap freezing, cryoprotectant permeation and subsequent cryopreservation.


RESULTS
Compared with the fresh tissue samples (immediately stabilized in RNAlater after collection), samples preserved by snap freezing exhibited the largest number of differentially-expressed genes. Some genes relate to neuron, drug addiction and drug binding, but the rest of differentially-expressed genes were functionally dispersive. Cryoprotectant permeation into tissue samples and subsequent cryopreservation via a rate-controlled freezing resulted in much less differentially expressed genes. Histological structures of tissue specimens were both well preserved by snap freezing and cryoproservation.


CONCLUSION
Snap freezing may not be as reliable as commonly considered. The pilot study demonstrates the feasibility of using cryopreservation to retain viable diseased tissues for multiple applications.