Which of the following is a sign of infusion-related reactions during chemotherapy?

Fever is considered a sign of infusion-related reactions during chemotherapy because it can indicate an immune response triggered by the infusion of the chemotherapy agent. These reactions could occur due to hypersensitivity to the medication, release of inflammatory cytokines, or other mechanisms that activate the body's immune system.

As chemotherapy drugs can have various effects on the body, the presence of a fever may suggest that the patient's body is reacting to the treatment, which could necessitate monitoring and possible intervention. Other symptoms like chills, rash, or difficulty breathing may also accompany fever in the context of infusion-related reactions, further highlighting its significance.

While headache, nausea, and weight gain may occur for a variety of reasons during chemotherapy, they are not specifically indicative of infusion-related reactions. Headaches could be due to dehydration or stress, nausea may result from the chemotherapy itself or its effects on the gastrointestinal tract, and weight gain may arise from changes in metabolism or fluid retention, but these are not direct indicators of an infusion reaction.