Uncovering the link between hormones and breast cancer

Background

Hormone Replacement Therapy (HRT) is a treatment containing synthetic hormones (analogues of oestrogen and progesterone) which is used to treat the symptoms associated with menopause. HRT increases a woman’s chance of getting breast cancer, and this risk is higher for women using HRT containing progesterone analogues compared to women taking oestrogen-only HRT.  Exactly how exposure to these hormones in HRT increases breast cancer risk is not clearly understood, and this is the focus of Professor Christine Clarke’s research.

The research

The researchers used a 3D model of a normal breast, along with tissue samples from women, to study how cells behave in the breast. They have found that the normal breast is made up of a range of cell types, and the cells most likely to become cancerous are those with the ability to grow rapidly. These cells are called stem cells or progenitor cells.

Using state-of-the-art technology, the team sequenced cells in the breast, allowing them to uncover unique variations between individual cells. They found that the stem cells in the breast contain progesterone receptors which can be stimulated by progesterone and stimulate normal breast cells to behave more like cancerous cells. They identified genes in the breast stem cells that are targeted by progesterone, and it is these genes that can get turned on and change the behaviour of breast cells. This finding has provided crucial evidence that there is a link between progesterone and the stem cells, which in turn explains how exposure to progesterone in HRT could lead to breast cancer.