Cryopreservation is a process that preserves tumor tissue by cooling the sample to very low temperatures. While it is scientifically possible to revive (or warm) cryopreserved tissue and develop PDX models from it, the success of that approach depends greatly on the method of cryopreservation, and the size (minimum one cubic centimeter) and condition of the tumor tissue sample. At Certis, we prefer to work with fresh tumor tissue (received and engrafted within 24 hours of biopsy or resection surgery) to maximize the likelihood of a successful study.