Mitotic index is simply a rate of cell division. It is relevant to
determine how aggressive a tumor is, or to determine whether or not a
mass of cells are cancerous.
Some 75% of all breast cancer tumors over-express(have an abnormally
high level of) estrogen receptor. Whether or not this is the 'root
cause' of breast cancer is difficult to determine. Estrogen receptor
acts as a regulator of gene expression by binding to 'estrogen
response elements' on DNA and recruiting various cofactors and
transcriptional machinery with which to convert DNA to mRNA to
proteins that enable cell growth. Having a high level of estrogen
receptor means that these cells can now produce certain proteins much
faster and grow much faster than normal--cancer.
Tamoxifen does not simply 'block' estrogen receptors. Upon binding to
estrogen receptor, it changes the shape of the receptor in such a way
that cofactors that normally enable estrogen receptor to stimulate
gene expression can no longer do so. As a result, tamoxifen blocks
Estrogen Receptor mediated gene expression and thus mRNA and protein.
This is a VERY simple view of estrogen receptor and tamoxifen. In
actuality this process is very complex expecially when taking into
account which proteins are involved in cell growth, tissue
selectivity, nongenotropic mechanisms, two different kinds of estrogen
receptor, and the various coactivators and corepressors. |
