Dr. Clark has pointed out since the early nineties that parasites can release growth factors that turn cells cancerous. She said so in her Disease Book in 1993, in her Cancer Book in 1995 and also in all later books, in more detail.
A recent report confirms that the human liver fluke releases growth hormones that can turn cells cancerous: http://www.sciencealert.com.au/news/20091210-19980.html. Interestingly, the article says that it is the "first research" showing parasite growth factors can cause abnormal cell growth... I guess they have not read aunt Hulda's books.
Not only has it been shown that these growth factors do cause cancer, but also that a very high percentage of those infected with the liver fluke are affected, namely every sixth infected person develops cancer.