Abstract 3639: DNA methylation in SYK, GSTP1, & FHIT genes: associations with parity and time since birth.
Authors: Kagwima Ruth N. , LLanos Adana A. , Brasky Theodore M. , Weng Daniel Y. , Freudenheim Jo L. , Shields Peter G. 
Published: August 2014

Introduction: Breast cancer risk is transiently increased following pregnancy; these tumors, referred to as pregnancy associated breast cancer (PABC) have poorer prognosis. As more women delay pregnancy until older age this increase in risk following pregnancy is projected to mean increased numbers of PABCs. Epigenetic events are important in the development and progression of cancer. Methylation status of specific genes may potentially be useful as screening targets in clinical practice. We examined DNA methylation for three genes of interest, Spleen tyrosine kinase (SYK), a non-receptor protein tyrosine kinase expressed in hematopoietic and non-hematopoietic breast epithelial cells, exhibiting tumor suppressor qualities, Fragile histadine triad (FHIT), encoding a protein involved in cell differentiation and apoptosis, and Glutathione S-transferase P1 (GSTP1), a phase II detoxification enzyme in most cell types acting on carcinogens, environmental pollutants, and drugs. We compared DNA methylation in these genes in breast tissues from healthy premenopausal women by parity status and time since last birth (nulliparous, &lt;5 years, &gt;10 years) to understand changes in methylation associated with recent pregnancy.

Methods: DNA samples were obtained from fresh frozen tissues of 81 premenopausal women undergoing reduction mammoplasty with no prior history of cancer except non-melanoma skin cancer. Genomic DNA was modified using EZ DNA Methylation Gold Kit and sequenced using Pyro Q-CpGTM Software. Two-sample t-tests and 1-way Analysis of Variance were used to examine differences in mean methylation in the three genes by parity status and time since last birth. Generalized linear regression models were used to compare mean methylation levels adjusted for age, race, menopausal status, and family history of breast cancer.

Results: Parous healthy premenopausal women had a higher adjusted mean methylation in all three genes than their nulliparous counterparts. Mean percent methylation of SYK (0.98 vs. 0.87; P=0.56) and FHIT (2.08 vs. 1.85, P=0.50) were 12% higher in parous versus nulliparous women. Methylation of GSTP1 was 7% higher among parous versus nulliparous women (0.70 vs. 0.65; P=0.82); however, differences were not statistically significant. For GSTP1, there was a suggestion of higher mean percent methylation among women who gave birth more recently (&lt;5 years: 0.93) versus births in the more distant past (&gt;10 years: 0.64) or nulliparous women (0.69; P=0.64). There were no clear differences by recency of birth for FHIT or SYK.

Conclusions: Mean percent methylation of SYK, GSTP1, and FHIT may be suggestive of changes in methylation among parous women, and for GSTP1, particularly higher DNA methylation among women who gave birth more recently. Given the small sample size, these findings are preliminary, and additional studies are needed to better understand methylation in PABC risk.

Citation Format: Ruth N. Kagwima, Adana A. LLanos, Theodore M. Brasky, Daniel Y. Weng, Jo L. Freudenheim, Peter G. Shields. DNA methylation in SYK, GSTP1, & FHIT genes: associations with parity and time since birth. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3639. doi:10.1158/1538-7445.AM2013-3639