One hallmark of cancer cells is their ability to resist programmed cell death. To investigate whether the patient’s colorectal tumour cells are defective in their ability to undergo apoptosis, the researcher performed a series of apoptosis assays. Patient-derived colorectal cancer intestinal epithelial cells (IECs) and normal IECs were treated with the chemotherapeutic agent camptothecin which is a topoisomerase inhibitor.