Cancer does not always respond to treatment. If the disease shows more than a slight increase in size or extent on or after treatment, this is termed progressive disease (PD).
Progressive disease implies that the administered treatment was not effective, and other treatments may be necessary to control the disease. When the disease is very extensive, doctors may give an individual the option of no further treatment.
Understand more about other terms used in assessing treatment response in the article How is treatment response described?