Of the list of cancer-fighting phytochemicals found in papaya leaf, Caffeic Acid has been shown as the most abundant of any in the papaya leaf, and significantly more abundant in the leaf than in any other part of the papaya plant including the fruit.
-Proximate Analysis, Antioxidant and Anti Proliferative Activities of Different Parts of Carica papaya Maisarah AM1, Asmah R1 and Fauziah O2, 1Department of Nutrition and Dietetics, Universiti Putra Malaysia, Malaysia 2Department of Human Anatomy, Universiti Putra Malaysia, Malaysia
What is significant about this is that Caffeic acid has shown effect on fighting specifically Prostate and Breast cancer. Its use is also as a complement to standard drugs like Tamoxifen. See the selected studies below.
Prostate Cancer:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0031286
Click to access documento-23.pdf
Breast Cancer:
http://www.mdpi.com/1420-3049/20/5/9242/pdf
http://www.mdpi.com/1420-3049/20/7/12576/pdf
Papaya Leaf Tea for Cancer 