Hello Robin 2021 and thanks for your question, 

Human and cancer biology is very complicated and an area of ongoing research, but In very simple terms there seem to be different things that can go wrong in and around cells which eventually lead to cancer developing. This is why breast cancer varies and isn't the same disease in everyone. Even breast cancers that have hormone receptors aren't all the same. This is the sort of subject that researchers are looking into to be able to explain more. Your husband might be interested in reading about some of the research that has looked into this on our science blog at the link below,

news.cancerresearchuk.org/.../increasing-the-resolution-on-breast-cancer-the-metabric-study

We do know that starting periods early and having a late menopause can increase the risk of breast cancer as can HRT taken after the age of the natural menopause (51 ish). So over someone's lifetime, longer oestrogen exposure relative to shorter expose, can increase breast cancer risk, but this isn't the whole story as although it increases risk, many people exposed to this risk will never develop breast cancer. 

In terms of staying healthy going forward, and apart from treatment, the advice is to achieve and maintain a healthy weight, limit alcohol intake to below 5 units a week and take regular exercise. And not to smoke.

I hope this helps. Call us if you want to talk anything over on  Freephone 0808 800 4040, we are around week days 9-5. 

Wishing you the best,

Julia