Progressive disease is defined as greater than what percentage increase in tumor burden or appearance of a new tumor?

• A. 50%
• B. 25%
• C. 75%
• D. 15%

Answer: (A)

Progressive disease is defined by a sizable growth in tumor burden. In the traditional WHO criteria used in many chemotherapy trials, progression is declared when there is a 50% or greater increase in the sum of the products of the two largest diameters for all measurable lesions, compared to the smallest sum observed or to baseline, or when any new lesion appears. Practically, you measure each lesion, calculate the sum of the products of its two longest diameters, and if that total grows by at least 50%, it signals progression. The appearance of new tumors also qualifies as progression regardless of changes in existing lesions. This 50% threshold is why the correct answer is 50%. Smaller increases (like 25% or 15%) would not meet the progression criterion under these criteria, while a larger change (75%) is more than the required threshold. Note that newer criteria (RECIST) use a 20% increase, with their own rules about new lesions, but the traditional standard reflected here centers on the 50% increase.