Hi,

Thanks for this link.

It is a little confusing but I don't think this article states that
breast cancer does not start in the breast.

When the article talks of breast cancer being a systemic disease, I
suspect it refers to the fact some breast cancer tumours don't just grow
 bigger and bigger until they reach other parts of the body. Instead,
even a small breast cancer tumour (which is located only in breast
tissue) may spread to other parts of the body via a few cancer cells
travelling through blood and/or lymph vessels. So, just removing the
tumour from the breast via surgery may not be sufficient to stop recurrence.

In the context of the article on lumpectomy versus mastectomy, perhaps
it was suggesting that the type of surgery isn't as important as whether
or not chemotherapy is done. Many years ago, radical mastectomy (removes
the muscle lining the chest as well as the breast) was the standard
treatment for breast cancer and chemotherapy not commonly used.
Currently, lumpectomy or modified radical mastectomy (where muscles are
left) are used in conjunction with chemotherapy.

Radiotherapy acts on local tumours only. However, by reducing or killing
local tumours you are also reducing the chance of these local tumours
spreading so you might argue that there is some potential systemic benefit.

I hope this helps.

Kim