Vietnamese researchers claim that 56% of breast cancer cells were inhibited by papaya leaf in the lab. The scientists also made note that the papaya leaf was harmless to the healthy cells. The control used was vitamin C, and papaya leaf showed a much higher antioxidant level with equal dosage.
Their research included tests on lung cancer (62% cells inhibited), and leukemia (60% cells inhibited).
-Research on Biological Activity of some Extracts from Vietnamese Carica papaya Leaves
Do Thi Hoa Vien, Phung Thi Thuy
ASEAN Journal of Chemical Engineering, vol. 12 no.2 (2012)