TURNING OFF CANCER 49CHART 3.1: TUMOR INITIATION BY AFLATOXIN INSIDE A LIVER CELL(2) AF is metabolized
by an enzyme.0~@t'YIDJ(3) A dangerous j
'-_p_rod_uct(_AF*_) is formed. -' ~---v ~ A~
(4) It attacks the
cell's DNA.
(5) Most damaged
DNA is repaired,
but sometimes ...Cancer Initiation
CancerousOJ"''
(6) A cell multiplies
before the damaged
DNA is repaired and
permanently damaged,
cancerous celis arise
After entering our cells (Step 1), most carcinogens do not, themselves, initiate the cancer
process. They first must be converted to products that are more reactive (Steps 2 & 3), with
the help of critically important enzymes. These carcinogen products then bind tightly to
the cell's DNA to form carcinogen-DNA complexes, or adducts (Step 4).
Unless repaired or removed, carcinogen-DNA adducts have the potential to create chaos
with the genetic workings of the cell. But nature is smart. These adducts can be repaired,
and most adducts are repaired fairly quickly (Step 5). However, if they remain in place
while cells are dividing to form new "daughter" cells, genetic damage occurs and this new
genetic defect (or mutation) is passed on to all new cells formed thereafter (Step 6). 17the byproducts of industrial processes, although small amounts may
be formed in nature, as is the case with aflatoxin. These carcinogens
genetically transform, or mutate, normal cells into cancer-prone cells.
A mutation involves permanent alteration of the genes of the cell, with
damage to its DNA.
The entire initiation stage (Chart 3.1) can take place in a very short
period of time, even minutes. It is the time required for the chemical
carcinogen to be consumed, absorbed into the blood, transported into
cells, changed into its active product, bonded to DNA and passed on to
the daughter cells. When the new daughter cells are formed, the process
is complete. These daughter cells and all their progeny will forever be
genetically damaged, giving rise to the potential for cancer. Except in rare
instances, completion of the initiation phase is considered irreversible.