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Policy#: 529-263

Title: ANIMAL USE GUIDANCE:Tumor Production in Rodents

Effective: 2/8/2021



This document provides general guidelines for experimentally induced and spontaneous development of neoplasia in rodents. Investigators should use this document as a reference when preparing their Animal Use Protocols. Office of the Campus Veterinarian (OCV) personnel may use this Guidance in determining a health case. The IACUC recognizes the difficulty in establishing specific limits on tumor burdens for rodents and that these general guidelines may not be applicable in all cases. However, the IACUC assumes that all projects will be compliant with these guidelines unless alternate procedures are clearly described and justified in the AUP and approved by the IACUC.


Each AUP involving tumor production in rodents must define a set of conditions under which the affected animals will be euthanized. Animals should be euthanized before their tumor burden becomes excessive and before the animals become debilitated. Use of survival time as an end point is rarely justifiable and should be avoided.

Rodents found with tumors unrelated to tumor production should be euthanized before their tumor burden becomes excessive and before the animal becomes debilitated.

The following general criteria for euthanasia should be used.

Solid Tumors

1. Tumor burden in rodents should not exceed 10% of the animal's body weight. In the case of a 25-gram mouse, this would represent a single nodule approximately 1.5 cm in diameter or multiple smaller tumors with a total volume equal to this. For rats, the tumor size limit is 2.5 cm in diameter or multiple smaller tumors with a total volume equal to this. Animals should be euthanized before tumors reach this size or if a subcutaneous tumor ulcerates prior to reaching this size. Some ulceration of intradermal tumors may be allowed if the animal remains in good condition. 

2. In some studies, either the tumor itself or anti-tumor therapies may cause the animal to lose weight. Adult animals should be euthanized if they lose 15% of their body weight, corrected for the weight of the tumor, or if growing animals fail to attain a weight 85% of non-tumor bearing animals. 

3. Depending on their type and location, some tumors may interfere with the function of vital organs or motor function. If animals show evidence of distress due to systemic illness (rough hair coat, dehydration, depression, severe diarrhea, anemia etc.) or problems with motor function (ambulation, eating, grooming, etc.) they should be euthanized regardless of the size of the tumor or body weight.

4. In addition to the daily health checks performed by the animal care staff, the Principal Investigator/research staff must be continually aware of the condition of the animals with induced tumors. In the case of very rapidly growing tumors or other situations in which the progression of clinical signs is likely to be rapid, the PI or research staff must examine the animals daily. Any animal that falls into one of the above categories must be reported to the PI who must examine and euthanize the animal within 24 hours unless such a condition is part of the approved Animal Use Protocol. If the PI is not responsive, the Campus Veterinarian may euthanize an animal deemed to be debilitated.

Hematological Tumors

1. The same guidelines as given in #2-4 above should be followed to ensure the adequacy of the animal's general condition. 

2. Peripheral blood cell counts should be used to establish limits that will not be exceeded. 

Other Tumors

Research or teaching situations that require the maintenance of animals with other tumors types may be proposed by submitting an Animal Use Protocol or amendment to the IACUC and will be considered on an individual basis. 

Guidelines for animals bearing ascites tumors are addressed in Guideline 529-261: Production of Monoclonal Antibodies Using Mouse Ascites Method.

Originally Adopted: 6/13/96; Updated: 12/9/04, 2/9/21