What is the most common symptom of a malignant tumor in small animals?

Weight loss is often recognized as a common symptom associated with malignant tumors in small animals. This can result from several factors that are typical in cancer cases. One significant reason is that tumors can alter the metabolic needs of the body, leading to an increased demand for energy. Malignant tumors may cause the body to expend more energy to support the tumor's growth and maintain essential physiological functions, leading to a negative energy balance and consequent weight loss.

Additionally, as the disease progresses, animals might experience a decrease in food intake due to physical discomfort or pain associated with the tumor, contributing further to weight loss. In many instances, weight loss becomes one of the most noticeable signs for pet owners, prompting them to seek veterinary advice.

While symptoms like a persistent cough, excessive thirst, and loss of appetite can certainly be associated with other conditions, weight loss is a consistent and general indicator of malignancy as it directly relates to the body's struggle against the cancerous process.