A novel method for freezing and storing research tissue bank specimens

Preserving small pieces of frozen tissue for possible future ancillary studies ("tumor banking") usually involves either placing a small piece of tissue in a cryovial and snap freezing it in liquid nitrogen or embedding and freezing the tissue in a block of cryopreservation medium, such as optimal cutting temperature (OCT) compound. The cryovial storage method leaves an irregularly shaped piece of tissue frozen to the side of the plastic vial, where it is exposed to air, subject to desiccation ("freezer burn"), and difficult to remove, but the vials are easy to store. The OCT method results in good morphological preservation, but yields a large awkwardly stored block from which it may be difficult to locate and recover small specimens. We have proposed a novel method of storing tissue bank specimens, the "capsule-freeze" method, which combines the advantages of OCT specimen preservation with those of cryovial specimen storage. Using this method, a tissue specimen is "snap-frozen" in OCT within a size "00" VCap pharmaceutical capsule, then the capsule is stored within a 1.5-mL cryovial. The specimen is harvested by simply cutting a slice out of the capsule and sealing the cut ends with OCT before their return to the freezer. The slice is then embedded en face within an OCT block before frozen sectioning. Morphological preservation is excellent, and the capsules are very easy to store. Occasional cracking that we found with the use of gelatin capsules is greatly diminished with the use of VCaps cellulose-walled capsules. The OCT can be easily removed by rinsing in cold 70% ethanol solutions. This method of tissue storage is ideal for the small specimens that are now commonly archived in these days of tissue sparing surgery.