"But we now know that the neighborhood (stroma) that the cancer cells live in also plays a critical role in determining whether a cancer or even a precancer like ductal carcinoma in situ (DCIS) will remain dormant or become invasive. Think of it this way: the stroma is like soil; cancer is a seed. In soil that support the seed (cancer cells), the seed (cancer cells) will flourish. In soil that is inhospitable, the seed (cancer cells) will never grow."

A discussion of HRT is in the link.