RECIST Tumor Response Calculator

The RECIST Tumor Response Calculator estimates tumor response categories based on baseline and follow-up measurements of longest diameters. This tool helps oncologists and radiologists quickly determine cancer treatment effectiveness by comparing size changes over time. Whether you are reviewing CT scans after chemotherapy, assessing immunotherapy results, or tracking clinical trial data, this tool provides objective response classification.

Enter the sum of the longest diameters of all target lesions measured at baseline
Enter the sum of the longest diameters of all target lesions at follow-up
Select whether lesions are measurable (using longest diameter) or non-measurable
Time period between baseline and follow-up measurements
Check if new lesions have appeared since baseline assessment

How Tumor Response Category Is Calculated

The Tumor Response Category is a standardized classification used to measure how well cancer treatment is working based on changes in tumor size. The calculation relies on the RECIST 1.1 criteria, which compares the sum of the longest diameters (SLD) of target lesions at baseline against follow-up scans.

((Follow-up SLD - Baseline SLD) / Baseline SLD) × 100

Where:

  • SLD = Sum of Longest Diameters

First, calculate the total diameter of all target lesions at the start of treatment to find the Baseline SLD. Next, measure the same lesions at a later date to get the Follow-up SLD. Finally, apply the percentage change formula to determine the exact degree of shrinkage or growth. This math-based approach ensures that medical professionals worldwide use the same objective standards to make critical treatment decisions.

What Your Tumor Response Category Means

Your Tumor Response Category indicates the biological success of your current cancer therapy in a clear, objective way. This result helps doctors decide if they should continue, change, or stop a treatment plan.

Complete Response (CR) means all target lesions have disappeared, indicating the treatment was very effective. Partial Response (PR) occurs when tumors shrink by at least 30%, showing the therapy is working and should likely continue. Progressive Disease (PD) happens if tumors grow by 20% or new lesions appear, often meaning the current therapy is not working. Stable Disease (SD) means tumors changed very little, which can be a positive outcome if the patient feels well.

Important

This tool measures linear diameter, not volume. A 30% decrease in diameter actually represents a much larger reduction in tumor cells, so the treatment may be more effective than the percentage alone suggests.

Disclaimer: This calculator is for informational purposes only and is not a substitute for professional medical advice. Always consult with an oncologist or radiologist to interpret scan results in the context of your overall health.

Monitor your response every 6 to 8 weeks to ensure the trends remain consistent before making major changes to your care plan.