Breast Cancer Epidemiology

Our main research area is breast cancer epidemiology including investigations of a variety of breast cancer risk and preventive factors as well as survivorship issues. Risk factors of particular interest include reproductive and hormonal factors, obesity, prescription drugs, breast cancer therapies including tamoxifen and genetics. Our group has particular focus on contralateral breast cancer and pregnancy-associated breast cancer.

A variety of common drugs has received interest as potential cancer preventive agents due to observations in experimental studies. However, for many of these drugs, no clear evidence for a protective effect on breast cancer has been found in epidemiologic studies. A possible explanation for this may be that it is difficult to identify anti-cancer effects of specific drugs in the general population due to different drug usage patterns and varying degrees of susceptibility to breast cancer.

Drug effects may be more easily assessed in studies of high risk women. One possibility is to investigate risk of contralateral breast cancer among breast cancer survivors, a group known to be susceptible to breast cancer. Therefore, we have a research project investigating use of various non-cancer drugs such as statins, NSAIDs and anti-histamines among women with breast cancer and risk of contralateral breast cancer. These efforts will be continued by pursuing findings among women with prior breast cancer in other groups of women at high risk of breast cancer.

Another research interest is hormonal factors and breast cancer including the possibilities to lower risk of breast cancer through surgical intervention. Removal of the ovaries leads to changes in sex hormone levels that may reduce the risk of breast cancer. However, this has not been clearly shown in epidemiologic studies. We have initiated a project that aims to provide more knowledge on how the risk of breast cancer is affected by removal of both ovaries, and furthermore how this surgical procedure affects type of breast cancer and the prognosis after breast cancer.

Hormones also play a key role in relation to pregnancy and breast cancer. Cancer is rarely diagnosed during pregnancy, however, among the cancers that coincide with pregnancy breast cancer is among the three most common ones. Studies on survival after breast cancer during pregnancy have provided inconsistent results, some showing a worse survival while others showing no difference in survival compared to non-pregnant women with breast cancer. If breast cancer is diagnosed shortly after a birth, a worse prognosis has been observed. Little is known about the exact time frame and about possibilities to reverse this pattern. These are research issues that our group will address in a project on pregnancy and breast cancer.

The research projects mentioned above are examples of projects that are carried out in our group. This is done together with external collaborators.

Selected publications:

Gottschau M, Kjær SK, Settnes A, Aalborg GL, Bens A, Jensen A, Munk C, Mellemkjær L: Ovarian Removal at or After Benign Hysterectomy and Breast Cancer: A Nationwide Cohort Study. Breast Cancer Res Treat 2020;181:475-485

Bens A, Dehlendorff C, Friis S, Cronin-Fenton D, Jensen Mb, Ejlertsen B, Lash T, Kroman N, Mellemkjær L: The role of H1-antihistamines in contralateral breast cancer: a Danish nationwide cohort study. Br J Cancer 2020;122:1102-1108

Langballe R, Frederiksen K, Jensen MB, Andersson M, Cronin-Fenton D, Ejlertsen B, Mellemkjær L: Mortality after contralateral breast cancer in Denmark. Breast Cancer Res Treat 2018;17:489-499

Brooks JD, John EM, Mellemkjær L, Lynch CF, Knight JA, Malone KE, Reiner AS, Bernstein L, Liang X, Shore RE, Stovall M, Bernstein JL: Body mass index, weight change, and risk of second primary breast cancer in the WECARE study: influence of estrogen receptor status of the first breast cancer. Cancer Med. 2016: 5(11), 3282-3291

Mellemkjær L, Papadopoulos FC, Pukkala E, Ekbom A, Gissler M, Christensen J, Olsen JH: Cancer incidence among patients with Anorexia Nervosa from Sweden, Denmark and Finland. PLoS.One. 2015: 10(5), e0128018