Gretchen L. Gierach, Ph.D., M.P.H.

Dr. Gretchen Gierach is interested in the study of the etiology of hormonally-related female cancers, particularly in the molecular mechanisms underlying breast carcinogenesis. Her interdisciplinary research program has a special emphasis on the molecular epidemiology of mammographic density, one of the strongest risk factors for breast cancer.

Epidemiologic Studies of Mammographic Density and Breast Cancer Risk

The tissue composition of the breast is reflected mammographically by the pattern of distribution of fibroglandular and fatty tissue. A higher component of fat results in lower mammographic density. Conversely, a higher proportion of fibroglandular tissue results in greater density. Studies have consistently demonstrated that high mammographic density is a strong breast cancer risk factor. Therefore, understanding factors that affect mammographic density and their underlying mechanisms are important, yet understudied, research questions.

The BREAST Stamp Project aims to characterize the radiologic, histologic, and molecular features of dense breast tissue and to understand how the microenvironment of dense breasts promotes neoplastic transformation of the breast epithelium. Data relating mammographic density to molecular markers of breast cancer are limited. To improve the clinical value of mammographic density as a risk marker, Dr. Gierach and her colleagues are conducting molecular epidemiologic studies to characterize dense and non-dense breast tissues.

In addition to addressing how molecular epidemiologic factors may influence mammographic density and its associated breast cancer risk, Dr. Gierach is also working to address other ways in which density may relate to breast carcinogenesis. In light of emerging evidence indicating that reductions in mammographic density may predict response to tamoxifen treatment, Dr. Gierach and her colleagues initiated a study within Kaiser Permanente Northwest to determine whether breast cancer patients who experience large reductions in density following tamoxifen treatment have an improved prognosis. They have also conducted the Ultrasound Study of Tamoxifen, in which they used novel ultrasound tomography methods to assess changes in volumetric breast density within the first year of tamoxifen therapy. These studies may provide support for future investigations evaluating change in mammographic density as a “biosensor” of factors that increase or decrease breast cancer risk.

Epidemiologic Studies of the Hormonal Etiology of Breast Cancer

Compelling evidence implicates endogenous hormones in breast carcinogenesis. To increase understanding of the role of hormones as etiologic factors in breast cancer, Dr. Gierach and her colleagues incorporate state-of-the-art methods to reliably and sensitively measure systemic hormones and characterize local hormone production in the breast to provide new etiologic insights. They also conduct epidemiologic studies to evaluate the influence of endogenous and exogenous hormones on both radiologic and histologic measures of breast tissue composition, which could help determine the extent to which hormones may influence breast cancer risk through modifying breast histology.

To address a critical need to better understand risk factors associated with second primary breast cancers in the growing population of breast cancer survivors, Dr. Gierach is conducting research within a breast cancer survivors' cohort to investigate the hormonal etiology of contralateral breast cancer. Within this cohort, she is also conducting ancillary studies integrating serial mammographic images and archival tissues to examine radiologic and molecular mechanisms associated with risk of contralateral breast cancer development.

Dr. Gierach earned both her M.P.H. and Ph.D. degrees in epidemiology from the University of Pittsburgh with a focus in cancer epidemiology and women’s health. She joined the Division as an NCI Cancer Prevention Fellow, continued as a tenure-track investigator and was awarded tenure in 2017. She served as Deputy Chief of the Integrative Tumor Epidemiology Branch from 2018 through 2020 and was appointed Chief in 2021. She also serves as chair of the Division’s Breast Cancer Working Group and co-chair of the DCEG Hormone Laboratory Advisory Committee.

Dr. Gierach is the recipient of the DCEG Molecular Epidemiology Research Funding Award, NCI Merit Award in Cancer Prevention Research Training, and Award to Advance Research on Cancers in Women from the NCI Office of Science Planning and Assessment and the NIH Office of Research on Women’s Health.