Which of the following is a method commonly used to monitor tumor response to treatment?

Monitoring tumor response to treatment is crucial for assessing the effectiveness of therapy and making any necessary adjustments. Regular blood tests and imaging studies are standard methods because they provide quantitative data about changes in tumor size, metabolic activity, and overall health status. Imaging studies, such as X-rays, ultrasound, or CT scans, allow for direct visualization of the tumor's response to treatment, while blood tests can reveal biomarkers or other indicators related to tumor activity.

Using physical examination alone might not provide the comprehensive data needed to accurately assess tumor response since it relies heavily on subjective observations, which can vary in accuracy. Owner observations of behavior changes, while important for understanding a pet's well-being, are also subjective and may not directly correlate with changes in the tumor itself. Endoscopic procedures can be useful in specific contexts (e.g., for tumors located in accessible areas), but they are not routinely used for ongoing monitoring across various types of tumors. Therefore, regular blood tests and imaging studies stand out as the most objective and reliable methods for monitoring treatment response.