Breast cancer is the most common form of cancer in women worldwide. In Switzerland alone, around 6,600 women are diagnosed each year. In about 70–80% of cases, these are hormone receptor-positive (HR+) tumors.
Breast cancer is the most common form of cancer in women worldwide. In Switzerland alone, around 6,600 women are diagnosed each year. In about 70–80% of cases, these are hormone receptor-positive (HR+) tumors.
This means the cancer cells have receptors—like tiny antennas—that respond to hormones such as estrogen and progesterone, which then influence how the cells behave. While the roles of estrogen and progesterone in both normal breast development and hormone-dependent breast cancers are well understood, one hormone remains underexplored: testosterone.
Though commonly associated with male biology, testosterone also plays a critical role in the female body. It's now gaining attention, especially in connection with hormonal contraceptives and hormone replacement therapies (HRTs). Many of these therapies include progestins—synthetic or natural hormones that mimic the action of progesterone. However, depending on their chemical structure, some progestins may also act like testosterone or block its effects. Progestins are often prescribed to protect the uterine lining from overstimulation by estrogen. But breast tissue is also hormone-sensitive and can respond differently—potentially increasing cancer risk. That's why it's crucial to study the specific effects of different progestins on breast cells.
To better understand the hormonal relationships, the team led by Prof. Dr. Cathrin Brisken at the École polytechnique fédérale de Lausanne is investigating how different hormones – individually and in combination – affect breast cells. Both healthy tissue and hormone receptor-positive breast cancer tissue are analyzed.
Initial results show that breast cells grew particularly strongly when treated simultaneously with estrogen, progesterone, and testosterone. A clear difference was also observed with synthetic progestins. A progestin with testosterone-like effects promoted cell growth and made the cells more aggressive – both in healthy and altered tissue. In contrast, an antiandrogenic progestin (i.e., one that inhibits testosterone) showed significantly less influence on growth.
These findings suggest that the type of progestin used can make a significant difference. However, the research is still at an early stage. Further studies and longer observation periods are needed to confirm these findings.
Millions of women use hormonal treatments—whether for birth control or menopause—for years or even decades. Yet, how these therapies affect breast cancer risk over the long term is still not fully understood. Current evidence indicates that testosterone may play a key role in hormone-driven cell growth, especially in phases of the menstrual cycle when estrogen, progesterone, and testosterone are naturally elevated. Prof. Brisken’s research aims to uncover the biological mechanisms behind these hormone interactions. In the future, this knowledge could help tailor hormonal therapies more precisely, minimizing cancer risks while maintaining their benefits.
Project number: KFS-5771-02-2023
| This research has been made possible by Swiss Cancer Research in collaboration with the Claudia von Schilling Foundation. |
