Tumor rodent models are critically important experimental cancer model systems where the goal is to study the growth and behavior of the tumors. This can lead to the development or refinement of novel therapies. Three different general rodent tumor model systems are in common use:

• Tumor inoculation:  Injections are used to propagate tumor cell lines and test treatments. Tumors can be transplanted orthotopically (at the origin site) or ectopically (eg. subcutaneously, intraperitoneally, or intravenously). For some tumor lines, engraftment may require further immunosuppression or low-level body irradiation, the use of immunodeficient mice (e.g. SCID or NSG), or a combination thereof.
• Spontaneous tumor development: Certain inbred, mutant, and genetically engineered mouse strains naturally develop tumors, making them useful for studying environmental and therapeutic effects, genetic mechanisms of tumor formation, and cancer treatments. These strains have a well-documented, high tumor incidence at specific ages. 
• Tumor induction:  This system relies on exposing the animal to a known and well-documented carcinogen with a predictable level of tumor induction. Formation of tumors using chemicals, radiation (eg. ultraviolet light), inflammation, infection, diet, etc.

• All injectable and/or implantable materials used for establishing tumors in animals generally must first be screened and evaluated for the presence of viral and bacterial contaminants. This is essential to prevent the introduction of murine infectious agents into the animal facilities which can result in the disruption or destruction of the current research or potentially affect other investigator colonies.  
• Prior to housing animals, an approved plan must be made with the Primary Site Veterinarian (PSV) for the facility in which you intend to conduct the research.
  • For housing at the College of Veterinary Medicine or College of Science, direct inquiries are made to CVM-LAR or CoS BRF/Tox. 
  • For other administrative units housing rodents, direct inquiries to the University Attending Veterinarian.
• All injectable human tumor lines require IBC review and approval prior to use. 
• The principal investigator should be familiar with the complications and disease resulting from the specific tumor cell injection.
• Intravenously injected tumor cells tend to localize in capillary beds, primarily in the lungs, potentially resulting in pulmonary distress and respiratory failure.  
• Intraperitoneal tumors may grow large with minimal impact or cause physiological changes that affect animal health and well-being. 
• Systemically injected tumors (intraperitoneal, intravenous, etc.) are more difficult to monitor. 
• Orthotopic, grafted tumors implanted in the correct anatomic location, animal models should be monitored for tumor growth and local/systemic complications. ie: rejection, infection, etc.
• Tumors should be injected in sites that don’t impair movement or normal behavior. Animals with impaired function should be removed from the study and euthanized per approved protocol method. 
• Some cancer models, ie: leukemia, do not result in solid tumor burden, however, overall general appearance and weight loss can be factors in determining tumor burden.

• Animals must be monitored, with all observations documented using a scoring system. Monitoring may include:
  • Body weight measurements
  • Tumor measures via calipers
  • Tumor burden score sheet
  • Clinical observations – recommended if there is no visible or palpable tumor.
• Daily monitoring, including weekends and holidays, is required for animals allowed to progress beyond clinical disease. 
• Tumors should be measured using calipers at least twice weekly after the tumor becomes visible. If the tumor is rapidly growing the measuring frequency should increase as needed to ensure that maximum tumor size is not exceeded. 
• Once a tumor reaches 10 mm in diameter in mice or 20 mm in diameter in rats, monitoring and tumor measuring may need to be increased in frequency.
• For internal (orthotopic) tumors, gentle palpation or advanced imaging can be used to aid in monitoring. If tumors are <10mm (about the size of a pea), more frequent monitoring may be necessary for tumor growth and overall well being. 
• For those models that do not have solid tumors, monitoring should be performed as necessary until signs of clinical disease. Once signs of disease manifest, monitoring should be increased.

• All monitoring must be documented and readily available upon request.
• Scoring sheets or checklists ensure consistent, accurate observations and documentation. A sample is provided, but any scoring system must be used, described, and approved in the protocol.

• Criteria for intervention must be outlined and approved in the protocol.
• Quantitative measures
  • % Body weight loss
  • Tumor calibrations
• Physiological signs
  • Increased respiration rate or labored breathing
  • Decrease fecal output, soft feces, or blood in feces
  • Urinary staining or scalding
  • Neurological abnormalities such as head tilt and or partial limb paralysis

Studies should ideally end when animals show clinical signs of disease, though this may conflict with research goals. Using death or moribundity as an endpoint requires prior justification and IACUC approval. The following guidelines for tumor endpoints are provided and exceptions to these guidelines need to have justification and approval by the IACUC. 

• Subcutaneous flank tumors should not exceed 20 mm for a mouse and 40 mm for a rat in any one direction. For multiple tumors, the longest diameter or total volume should guide endpoint decisions. Some tumor lines may require a smaller size endpoint.
• Animals with tumor-related ulceration, infection, or necrosis 
• Tumors that interfere with ability to obtain food/water or impair quality of life (eg. inability to urinate, walk, etc) 
• Body condition scoring (less than 2).
• Neurological abnormalities such as full hind limb paralysis or loss of self righting reflex.
• When orthotopic (internal) tumors  interfere with normal biological and physiological functions. 
• Ocular proptosis (leukemias and cranial tumor models)
• Weight loss >15% of baseline and general overall kept appearance should be indicators of tumor burden in those models without physical tumors. ie: leukemias, etc

Animals that are inoculated with an orthotopic or leukemia model should be monitored via a score system. An example of scoring systems is located on the Resources appendix at the bottom.  Evaluate the animal in each of the categories and assign a score. The impact scoring system is quite subjective. Therefore, investigators should strive to have the same individual make and score the observations

Clinical observations to notate:

• General appearance: Dehydration, weight loss, abnormal posture, hypothermia, abdominal distention, swelling, vocalization
• Skin and fur: Discoloration, urine stain, redness, blueness, jaundice, wound, abscess, bloody or purulent discharge
• Head: Enlarged eyes, small eyes, eye discharge, head tilt, nasal discharge, drooling
• Respiration: Sneezing, rattle, abnormal breathing
• Urine: Discoloration of back/fur, blood in urine, excessive or no urination
• Feces: Discoloration of back/fur, blood in feces, diarrhea
• Genital area: Prolapses, constriction of penis
• Locomotion: Hyperactivity, hypoactivity, impaired movement, poor coordination, circling, tremors