To avoid slow growth and variation between animals, Certis uses both seed cohorts and pre-study cohorts.

Seed Cohorts
We implant cryopreserved tumor fragments in an initial seed cohort of mice, measuring and monitoring tumor growth. Cryopreserved tumor fragments typically grow slower and have greater growth variability than live, warm tissue. When enough mice in the seed cohort show substantial tumor growth, on average between 500-1000mm3, those seed tumors are excised from the mice, and re-implanted into a pre-study cohort of mice.

Pre-Study Cohorts
Reimplanting live, warm tissue in a pre-study cohort of mice (plus overages) allows for faster take rates, predictable growth kinetics, tighter randomization volumes and less variation among groups on Day Zero (D0), when we start dosing your mouse avatars, after randomization.

Our PDX studies are initiated using only a few warm tumors with comparable growth kinetics, to ensure that your test groups behave predictably, and the only variables introduced are the test agent being assessed for efficacy.