High testosterone boosts risk of breast cancer?

A study published in the Journal of the National Cancer Institute suggests that high serum levels of testosterone in premenopausal women can substantially increase the risk of breast cancer.  

The case-control study shows those in the highest quartile of serum levels of testosterone, compared with those in the lowest quartile, were 73% more likely to be diagnosed with breast cancer, indicating that high testosterone may increase the risk of breast cancer.  Similarly, androstenedione and DHEAS were also linked to elevated risk of breast cancer.  

Caution needs to be exercised when interpreting the results of the study.  The study does not seem to provide data on the serum levels of female sex hormones like estrogen, which is known to promote the development and progression of breast cancer.  

Other studies have found that actually high levels of testosterone are protective against breast cancer and the ratio of estrogen to androgen is important in determining the risk of breast cancer.  In the current study, the association between high levels of testosterone and elevated risk of breast cancer may only make sense when high levels of estrogen were also present in women with high levels of testosterone.  Unfortunately, authors did not reveal the data on estrogen.

According to the literature, testosterone therapy was used 40 years ago to treat breast cancer, but discontinued for some reason.  Testosterone, by logics, should protect against breast cancer.  Indeed, testosterone when used in women with advanced breast cancer extended their survival as shown in at least one study.

Think about this extreme case.  Men have high levels of testosterone and relatively low levels of estrogen and they are much less likely to develop breast cancer than women!  

One thing women with high estrogen and low testosterone can do to lower their risk of breast cancer is increase their physical activity.  Physical activity can lower estrogen and reduce their risk of breast cancer.  (David Liu, PHD)

Reference

Rudolf Kaaks, Franco Berrino, Timothy Key, Sabina Rinaldi, Laure Dossus, Carine Biessy, Giorgio Secreto, Pilar Amiano, Sheila Bingham, Heiner Boeing, H. Bas Bueno de Mesquita, Jenny Chang-Claude, Françoise Clavel-Chapelon, Agnès Fournier, Carla H. van Gils, Carlos A. Gonzalez, Aurelio Barricarte Gurrea, Elena Critselis, Kay Tee Khaw, Vittorio Krogh, Petra H. Lahmann, Gabriele Nagel, Anja Olsen, N. Charlotte Onland-Moret, Kim Overvad, Domenico Palli, Salvatore Panico, Petra Peeters, J. Ramón Quirós, Andrew Roddam, Anne Thiebaut, Anne Tjønneland, Ma Dolores Chirlaque, Antonia Trichopoulou, Dimitrios Trichopoulos, Rosario Tumino, Paolo Vineis, Teresa Norat, Pietro Ferrari, Nadia Slimani and Elio Riboli, Serum Sex Steroids in Premenopausal Women and Breast Cancer Risk Within the European Prospective Investigation into Cancer and Nutrition (EPIC), Journal of the National Cancer Institute, 2014.