We have studied the role of lifestyle factors on subtypes of breast cancer.
We confirmed that postmenopausal hormone use increases risk of hormone receptor positive disease (Ursin 2002), but that breastfeeding protects against both hormone receptor positive and receptor negative subtypes (Ursin 2005, Ma 2006, Lord 2008). This has since been replicated in more detailed studies of breast cancer subtypes.
We have studied various correlates of diet and body mass in women. Most recently we described the association with body mass and breast in pre/perimenopausal women; it takes time before the well known protective effect in the premenopause becomes causative (Berstad 2010).
We developed our own computer-assisted method for determining mammographic density, a breast cancer biomarker (Ursin 1998), and showed that this is a strong predictor of breast cancer risk (Ursin 2003). We have shown that:
- There is a strong familial component to mammographic density, but that the genetic component may be smaller than expected (Ursin 2009).
- Certain dietary components can influence density, in particular soy intake (Ursin 2007)
- Hormone therapy in a randomized placebo-controlled trial increases density (Greendale 2003), the changes are related to serum hormone levels (Ursin 2005), and certain genetic variants may modify this change.
- Women with the largest increase in density in the Women’s Health Initiative trial were the women with the highest risk of cancer (Byrne, Ursin et al., forthcoming).