Screening and prevention in women at increased breast cancer risk

Abstract

The most frequent cancer among women in the Western world arises in the breast accounting for over 1.7 million new cases in 2012, a number which is still rising. Much attention is paid to the discovery of new ways to prevent breast cancer, as is the search for new treatment modalities with a minimum amount of treatment related toxicities. In the research described in this thesis, the focus has been on using the ductal mammary system as a new avenue for early detection and innovative treatment.

In the first part of this thesis, we focus on methylation and nipple fluid. In Chapter 2, we found that in particular AKR1B1 and TM6SF1 were significantly differentially methylated in normal versus malignant breast tissues, and that these genes might serve as candidate methylation biomarkers in nipple fluid. Since intratumor methylation heterogeneity methylation might lead to sampling bias when used as a biomarker for breast cancer detection, we performed methylation analysis on multiple spatially separated breast cancer samples in Chapter 3. We demonstrated that clonal epigenetic heterogeneity is present within most primary breast carcinomas and can lead to aberrant methylation status calling. To further explore the use of nipple fluid as a screening method, we performed a feasibility study to evaluate the potential of repeated aspirations in Chapter 4. In a large group of women at increased breast cancer risk, repetitive aspirations appeared to be feasible and safe. Independent predictive factors for successful nipple fluid aspiration were premenopausal status, spontaneous nipple discharge, smaller breast size, bilateral oophorectomy and previous use of hormone replacement therapy or anti-hormonal treatment. In Chapter 5, we validated the methylation status of a gene panel in nipple fluid of healthy women, women with sporadic breast cancer and their contralateral breasts. Cancerous and healthy nipple fluid could be discriminated based on a multivariate model with methylation levels of AKR1B1, ALX1, RASSF1A and TM6SF1. Although within-patient differences between cancerous and contralateral nipple fluid samples were less prominent, cancerous nipple fluid contained increased levels of methylation of tumor suppressor genes that potentially could serve as a biomarker for early breast cancer detection.

In the second part of this thesis, we continued with the intraductal approach. In Chapter 6, we showed that intraductal cisplatin treatment leads to a uniform reduction of the epithelial mammary cells and thereby prolongs breast tumor-free survival in a conditional Brca1-associated mouse model. Intraductal based treatment is less invasive than current prophylactic strategies used in BRCA1-mutation carriers and may therefore be an alternative prophylactic therapy.

The final part of this thesis describes the regulatory function of the adherens junction protein p120 in cytokinesis. The classical role described for p120 is the maintenance of epithelial integrity by stabilization of E-cadherin. Moreover, p120 can inhibit activation of the Rho GTPase RhoA. In Chapter 7, we demonstrate a new tumor suppressive role of p120. Loss of p120 induces RhoA-dependent cytokinesis failure leading to binucleation and chromosomal instability in cancer. This function depends on an E-cadherin-independent N-terminal interaction with the centralspindlin component MKLP1.