BACKGROUND

The Guide for the Care and Use of Laboratory Animals (the Guide, NRC 2011) states that tumor models require special consideration of humane endpoints (p. 27). This Standard Operating Procedure (SOP) provides detailed descriptions of procedures to be followed unless alternate procedures have been outlined in an IACUC Protocol Application. If an investigator wishes to deviate from the approved SOP, all changes must be outlined and justified in the protocol application (approval of the protocol indicates approval of the deviation from the SOP for that project only).

IACUC Policy

Subcutaneous Tumors (visually monitored)

1. Prior to the approximate time when tumor growth becomes evident, animals are monitored on a periodic basis. The frequency will depend on how soon tumor growth will become evident following injection. In most cases, once a week should be adequate. If the approximate time of tumor growth is not known, the animals in the initial group are very carefully monitored (i.e., every other day). The frequency of monitoring must be outlined in the protocol. 

2. Once tumor growth has been identified, animals are monitored at least twice weekly. Some tumor lines will require daily checks. It is best practice to maintain records of tumor measurements. Frequency of measurement is dependent on tumor volume doubling time and overall animal condition. The frequency of monitoring must be outlined in the protocol.

3. It is the laboratory's responsibility to adhere to endpoints described in this SOP and approved in the protocol.

4. The monitoring frequency is such that animals are euthanized as soon as the following signs develop; death is not an acceptable endpoint. Any ONE of the criteria below could require euthanasia:

• Total tumor burden approaches 5-10% of the animal's body weight (tumor would be approximately 1.6 cm in diameter for a 20g animal or 1.8 cm for a 30g animal). The burden is additive for animals with multiple tumors.
  • Two of the most commonly used formulas for determining each individual tumor volume are:
    • 1. mg = length (mm) x width2 (mm2) / 2
    • 2. volume (V) = length (mm) x width (mm) x depth (mm) x Ï€/6 (where V is equivalent to mg)

• Body Condition Score (BCS) <2/5

• Tumor(s) that interferes with locomotion, eating or drinking

• Necrotic tumors, unless scientifically justified

• Presence of ulcerated tumor*

*Studies should be designed so that data has been obtained prior to tumors developing ulcerations. Animals with ulcerated tumors must be euthanized unless an exemption is approved in the protocol. The exemption must be scientifically justified and should include a plan for increased monitoring frequency and clearly defined endpoints. For animals exhibiting ulcerated tumors, the total tumor burden cannot exceed 1gm or 5% body weight, whichever is less, as long as they are asymptomatic.

5. For human tumors, if an animal dies unexpectedly, show signs or symptoms of illness or tumor ulceration is observed, refer to the Wayne State University IBC Memo: Reducing Biohazard Exposure Risks When Working with Human Cell Lines and Human Tissue in Animal Projects.

6. Euthanize animals using the method as outlined in the approved IACUC protocol.

Internal or Orthotopic Tumors (cannot be visually monitored)

1. Prior to the approximate time when tumor growth begins, animals are monitored on a periodic basis. The frequency will depend on how soon tumor growth begins following injection. Monitoring should range from daily to weekly. If the approximate time of tumor growth is unknown, the animals in the initial group are very carefully monitored (at least every day is recommended). The frequency of monitoring must be outlined in the protocol.
2. Once the animal exhibits signs that can be attributed to the tumor, the animal needs to be monitored with increased frequency. The frequency will depend on the rate of growth, organ affected, and type of tumor. This frequency must be outlined in the protocol. 
3. The monitoring frequency is such that animals are euthanized as soon as the following signs develop; death is not an acceptable endpoint. The criteria for euthanasia (one of the following):

• Total tumor burden approaches 5-10% of the animal's body weight (percentage depends on the tumor's internalized location higher limit needs justification provided in protocol)
• Lethargy
• Animal unable eat, drink or ambulate
• Respiratory distress or abnormal respiratory pattern
• Body Condition Score (BCS) <2/5

4. Euthanize animals using the method as outlined in the approved IACUC protocol.

Approved: February 2007

Revisions Approved: August 2008, December 2012, October 2017, June 2023

Reviewed: October 2019