TURNING OFF CANCER 65Not only are these effects substantial, but we also discovered a net-
work of complementary ways by which they worked.
Next question: can we generalize these findings to other cancers and
to other carcinogens? At the University of Illinois Medical Center in
Chicago, another research group was working with mammary (breast)
cancer in rats.^49 -^51 This research showed that increasing intakes of ca-
sein promoted the development of mammary (breast) cancer. They
found that higher casein intake:- promotes breast cancer in rats dosed with two experimental car-
cinogens (7,12-dimethybenz(a)anthracene (DBMA) and N-ni-
troso-methylurea (NMU)) - operates through a network of reactions that combine to increase
cancer - operates through the same female hormone system that operates in
humans
LARGER IMPLICATIONSAn impressively consistent pattern was beginning to emerge. For two
different organs, four different carcinogens and two different species,
casein promotes cancer growth while using a highly integrated system
of mechanisms. It is a powerful, convincing and consistent effect. For
example, casein affects the way cells interact with carcinogens, the way
DNA reacts with carcinogens and the way cancerous cells grow. The
depth and consistency of these findings strongly suggest that they are
relevant for humans, for four reasons. First, rats and humans have an
almost identical need for protein. Second, protein operates in humans
virtually the same way it does in rats. Third, the level of protein intake
causing tumor growth is the same level that humans consume. And
fourth, in both rodents and humans the initiation stage is far less im-
portant than the promotion stage of cancer. This is because we are very
likely "dosed" with a certain amount of carcinogens in our everyday
lives, but whether they lead to full tumors depends on their promotion,
or lack thereof.
Even though I became convinced that increasing casein intake pro-
motes cancer, 1 still had to be wary of generalizing too much. This was an
exceptionally provocative finding that drew fierce skepticism. But these
findings nonetheless were a hint of things to come. I wanted to broaden
my evidence still more. What effect did other nutrients have on can-