What should an in vivo study plan include?
A plan that a scientific team, a statistician and a contract research organization can all work from answers the same questions a good paper later has to report. The ARRIVE 2.0 guidelines set out an Essential 10 for animal research: study design, sample size, inclusion and exclusion criteria, randomization, blinding, outcome measures, statistical methods, the animals, the procedures and the results. Planning against that list early means nothing important is decided by default on the first day of dosing.
The planner groups your answers into the sections a study outline normally has:
- Objective and the primary endpoint it will be judged on
- Model: type, species, strain, sex, age and number of models
- Treatment groups, including vehicle and any reference compound
- Dose, route and frequency
- Endpoints and when each is measured
- Timeline, including tumor take or acclimatization time
- Open decisions and the checks every team should confirm
CDX, PDX or syngeneic: which model answers your question?
Cell line-derived xenografts (CDX) grow an established human cancer cell line in immunodeficient mice. They are reproducible and quick to set up, which suits ranking compounds and dose finding. Patient-derived xenografts (PDX) implant tumor tissue taken from patients, and are widely used because they keep more of the original tumor's biology than long-established cell lines; Hidalgo and colleagues review their strengths and limits. Syngeneic models grow a mouse tumor in immunocompetent mice of the matching strain, so the immune system is intact, which is why they are used for immunotherapy questions.
The planner does not choose a model for you. It records the choice, or flags it as undecided, and adds model-specific checks: characterization data for PDX models, host strain and immune readouts for syngeneic ones. For PDX-specific design, including how many models to use, see the PDX Study Planner.
How many animals per group does an in vivo study need?
That depends on the primary endpoint, how variable it is in your model, and the size of effect that matters to you, so it should come from a statistician's power calculation rather than from a planning tool. ARRIVE 2.0 asks you to report the number of experimental units per group and in total, and to explain how that number was chosen. The experimental unit is not always the animal: it can be a cage or a litter.
The NC3Rs Experimental Design Assistant is a free tool that supports sample size calculation and randomization. This planner deliberately does not suggest a number. If you enter models, groups and animals per group, it shows the product and the assumptions behind it, so you can check the total against your ethics approval and your budget.
Which endpoints and humane limits should be agreed before dosing?
Tumor volume measured by caliper, body weight and clinical signs are the usual in-life measures in oncology efficacy studies, with terminal tumor weight and tissue collection at the end. Agree exactly how each is measured, how often, and how the result will be summarized. Several tumor growth inhibition formulas are in use, so name the one you will report before the study starts.
Humane endpoints belong in the plan, not in a later amendment. The OBSERVE consensus guidelines (Nature Protocols, 2024) and the UK NCRI guidelines (Workman et al., 2010) cover clinical signs to monitor, tumor burden limits and humane endpoints for rodent cancer models. In the EU, Directive 2010/63/EU makes Replacement, Reduction and Refinement a legal requirement and requires each animal project to be authorized in advance.
From plan to quotes
Copy or print the plan and share it with your team. When it is ready to go out, turn it into a request with the CRO RFP Generator, or compare quotes from vetted in vivo pharmacology suppliers on BioBridgeX. For budgeting, the in vivo efficacy cost guide at costs in vivo efficacy study costs lists published price ranges by model type.
Frequently asked questions
Does the planner recommend how many mice I need?
No. Group size should come from a power calculation for your primary endpoint, done with a statistician. The planner only multiplies the numbers you enter and shows the assumptions, so the total is arithmetic, not a recommendation.
How is the total number of animals calculated?
Total animals = number of models x treatment groups x animals per group. It assumes every model runs every group, every group has the same number of animals, and it excludes satellite, pharmacokinetic, spare and replacement animals, which you should add separately.
What is the difference between a syngeneic model and a xenograft?
A xenograft grows human tumor cells or tissue in immunodeficient mice. A syngeneic model grows a mouse tumor in immunocompetent mice of the same strain, so the immune system is intact. That makes syngeneic models the usual choice when the question involves the immune response.
CDX vs PDX: what is the difference?
A CDX model uses an established human cancer cell line; a PDX model uses tumor tissue taken directly from a patient. CDX models are quicker and more uniform. PDX models keep more of the patient tumor's characteristics but take longer to expand and vary more between models.
What should I agree with a CRO before an efficacy study starts?
The primary endpoint and how it is measured, the model and animals, group design and allocation method, dose formulation and schedule, humane endpoints, the analysis method, the data and report format, and who owns the raw data. The planner's checklist lists these so none is left to default.
Which ethics approval does an in vivo study need?
It depends on where the work runs, for example an IACUC protocol in the US, or a project licence with AWERB review in the UK. In the EU, Directive 2010/63/EU requires prior authorization of each project. The CRO running the study holds the local approvals, but your design must fit within them.
Is anything I type stored or shared?
No. The planner runs entirely in your browser. Nothing you enter is saved, sent to BioBridgeX, put in the page address or passed to analytics or AI services. Closing or refreshing the page clears it, so copy or print the plan before you leave.
Is the generated plan a protocol?
No. It organizes the requirements you entered into a structured outline and lists what is still undecided. It is not a validated protocol, it does not recommend sample sizes, and it does not establish GLP, GMP or regulatory compliance. Have the plan reviewed by qualified scientific, statistical, ethical and regulatory experts.
Related free tools
- PDX Study Planner: Indication, biomarkers, number of models, groups, dosing schedule, tissue collection and analysis in a PDX outline.
- Pharmacokinetic (PK) Study Planner: Species, dose levels, routes, groups, sampling time points, matrix and PK parameters as a PK study outline.
- In Vitro Assay and Screening Planner: Assay type, cell models, compounds, concentration series, controls, replicates and readout as an organized assay plan.
- All study planners and every free tool on BioBridgeX.
Sources
- Percie du Sert N et al. The ARRIVE guidelines 2.0. PLoS Biology 2020;18(7):e3000410
- Percie du Sert N et al. The Experimental Design Assistant. PLoS Biology 2017;15(9):e2003779
- Hidalgo M et al. Patient-derived xenograft models: an emerging platform for translational cancer research. Cancer Discovery 2014;4(9):998-1013
- De Vleeschauwer SI et al. OBSERVE: guidelines for the refinement of rodent cancer models. Nature Protocols 2024;19(9):2571-2596
- Workman P et al. Guidelines for the welfare and use of animals in cancer research. British Journal of Cancer 2010;102(11):1555-1577
- Directive 2010/63/EU on the protection of animals used for scientific purposes
This planner organizes requirements. It is not a validated protocol, does not recommend sample sizes, and does not establish GLP, GMP or regulatory compliance. Review every plan with qualified scientific, statistical, ethical and regulatory experts. Facts on this page last checked 27 October 2026.
Compare quotes from vetted In Vivo Pharmacology & Efficacy suppliers on BioBridgeX. Free for buyers. Planning is optional: these tools work without an account, and nothing you enter is shared.