Genotyping and phenotyping of distant breast cancer metastases

Abstract

With 1.7 million new cases annually worldwide, breast cancer is the most common cancer in women. Approximately 30% of breast cancer patients eventually develop recurrent or metastatic disease, which remains essentially incurable. A detailed (epi)genetic and phenotypic characterization and understanding of metastatic tumors is a prerequisite for the development of models that can predict which patient will develop metastatic disease, to personalize systemic treatments and to prevent such metastases from becoming clinically manifest. In this thesis we discuss the concordance and discordance of divergent genotypic and phenotypic characteristics in paired primary tumors and distant breast cancer metastases. In the first part of this thesis, we focused on the (epi)genetic similarities and differences between primary breast tumors and paired distant metastases. We compared the mutational profiles of actionable cancer targets, we explored APOBEC3B (Apolipoprotein B editing catalytic subunit 3B) mRNA expression, we performed promoter hypermethylation profiling of tumor suppressor genes and we studied global miR (microRNA) expression patterns of multiple metastases per patient. The detected pattern of somatic mutations, copy number alterations, APOBEC3B mRNA and miR expression was largely retained in the metastasis relative to the primary breast tumor. Furthermore, a significant amount of novel alterations and/or an increase of alteration frequency was demonstrated. These additional aberrations may be provoked by the distant microenvironment or systemic treatments and may confer an added survival advantage. The second part described divergent phenotypic biomarkers in primary breast tumors and paired distant metastases that have the potential to become markers for treatment response, therapeutic targets or prognostic or diagnostic factors. We first reviewed the frequency of receptor conversion (the change in hormone and HER2 receptor status). Second, we studied the influence of three routinely used decalcifying agents on assessment of hormone and HER2 receptor status and DNA/RNA quality in bone metastases. Thereafter, we evaluated the frequency of receptor conversion in primary breast carcinomas and their matched malignant peritoneal and/or pleural effusions, we presented a novel mechanism of acquired anti-estrogen resistance in metastatic breast cancer and we examine GRPR, CXCR4 and SSTR2 mRNA expression levels of primary tumors and paired metastases. In contrast to the relatively stable (epi)genetic aberrations mentioned in part one of this thesis, the phenotypic markers tested in part two showed high discordance levels between primary breast tumors and paired distant metastases. It could be that the proteins we tested were more prone to selective pressure of adjuvant therapies than mutations and epigenetic variations. Ideally, in cancer care, we need a predictable biomarker pattern for therapeutic targeting that can help many patients at the same time. However, we showed that no patient and no tumor looks alike and the key in targeted treatment must therefore be a tailored approach per tumor and per patient.