Scientists continue to work to define the reason why proteases like the ones in papaya leaf (papain and chymopapain) have shown to slow the growth of tumors.
“…we have discovered that proenzyme therapy, mandated first by John Beard nearly one hundred years ago, shows remarkable selective effects that result in growth inhibition of tumor cells with metastatic potential.”
-Proenzyme therapy of cancer. Novak JF, et al. Anticancer Res. 2005 Mar-Apr.
John Beard, a Scottish doctor, proved the effect of trypsin (a protease taken from a young cow) on halting the growth of tumors in humans by injecting part of the Pancreas of the young cow straight into human tumors.
Papain has been shown to be more powerful of a protease than trypsin.