Maybe it is, but I don't think that is the reason.

There is a difference between what causes cancer (eg carcinogens) and what
promotes the growth of tumours (eg hormones).  Whatever the cause, we know
that most cancers achieve rapid growth by multiplying the number of
receptors for various factors, in the case of breast notably Estrogen (ER)
and Human Epidermal growth factor (HER)

Once you've got a cancer, taking away the cause (or causes) has no effect on
the existing cancers, it just stops more cancers starting.  You have to
actively kill off the cells (chemotherapy, radiotherapy), or at least stop
them dividing (hormone therapy).

Of course hormone therapy is rarely a complete approach to destroying
cancer, it won't reverse well established aggressive tumours, but it can be
very effective in making individual cancer cells and small clusters of cells
go dormant for a long long time, long enough for the immune system to pick
them off.  And in this way it reduces the number of recurrences perhaps by
half.

It seems more likely that the anti-fungal action would be more relevant to
protecting against the formation of new cancers.  We know that breast cancer
survivors are at a relatively high risk of getting another independent
primary cancer.  We know Tamoxifen does reduce that risk quite a lot, and it
may not be all due to cancers which form but do grow.  There is no obvious
reason why estrogen deprivation alone should stop the formation of cancers.

Tim

Su-Texas

Whew!  Thank you for adding that Su.  I sure don't need to be telling my
onc I refuse to try Tamoxifen.   So now I can take it with peace of
mine, right!

Bea