Define a humane endpoint in a mouse study.

• A. A predefined criterion defined by the study protocol that requires euthanasia at a predetermined time.
• B. A lack of any signs of distress, indicating continued participation.
• C. A predefined criterion indicating that an animal should be removed from the study to prevent further suffering or distress.
• D. A spontaneous decision by the researcher to end the study for any reason.

Answer: (C)

Humane endpoint is a predefined criterion within the study protocol that signals an animal should be removed from the study to prevent further suffering or distress. This concept centers on welfare: if an animal shows signs of pain, severe distress, or morbidity beyond what’s ethically acceptable, continuing the procedures would harm the animal, so the protocol requires withdrawal or euthanasia. Endpoints are set in advance and reviewed by oversight bodies to ensure decisions are consistent and based on welfare, not on the investigator’s personal preference or a fixed schedule. Examples include substantial weight loss, inability to access food or water, severe lethargy or impairment, or significant tumor burden that causes pain or suffering.