54 THE CHINA STUDYPROTEIN AND PROMOTION
To go back to the lawn analogy, sowing the grass seeds in the soil was the
initiation process. We found, conclusively, through a number of experi-
ments, that a low-protein diet could decrease, at the time of planting,
the number of seeds in our "cancerous" lawn. That was an incredible
finding, but we needed to do more. We wondered: what happens during
the promotion stage of cancer, the all-important reversible stage? Would
the benefits of low protein intake achieved during initiation continue
through promotion?
Practically speaking, it was difficult to study this stage of cancer be-
cause of time and money. It is an expensive study that allows rats to live
until they develop full tumors. Each such experiment would take more
than two years (the normal lifetime of rats) and would have cost well
over $lOO,OOO (even more money today). To answer the many ques-
tions that we had, we could not proceed by studying full tumor develop-
ment; I would still be in the lab, thirty-five years later!
This is when we learned of some exciting work just published by oth-
ers3l that showed how to measure tiny clusters of cancer-like cells that
appear right after initiation is complete. These little microscopic cell
clusters were called foci.
Foci are precursor clusters of cells that grow into tumors. Although
most foci do not become full-blown tumor cells, they are predictive of
tumor development.
By watching foci develop and measuring how many there are and how
big they become,32 we could learn indirectly how tumors also develop
and what effect protein might have. By studying the effects of protein
on the promotion of foci instead of tumors we could avoid spending a
lifetime and a few million dollars working in the lab.
What we found was truly remarkable. Foci development was almost
entirely dependent on how much protein was consumed, regardless of how
much aflatOXin was consumed!
This was documented in many interesting ways, first done by my
graduate students Scott Appleton^33 and George Dunaip4 (a typical com-
parison is shown in Chart 3.4). After initiation with aflatoxin, foci grew
(were promoted) far more with the 20% protein diet than with the 5%
protein diet. 33,34
Up to this point, all of the animals were exposed to the same amount of
aflatoxin. But what if the initial aflatoxin exposure is varied? Would protein