Stromal collagens in colorectal cancer and in colorectal liver metastases tumour biological implications and a source for novel tumour markers

Abstract: Background: Colorectal cancer (CRC) remains one of the leading causes of cancer-related mortality. About 50 % of patients with CRC will develop subsequent liver metastases (CLM). The survival for untreated CLM is only a few months and liver resection provides the only chance for a lasting cure. It is therefore essential to detect CLM early, enabling successful surgical resection and achieving a long-term cure. There are no optimal tumour markers for CRC or CLM. The best marker available is Carcinoembryonic Antigen (CEA), a marker found elevated in about 50-60% of patients with CLM, but also in many other conditions. The main focus of cancer research has been on the malignant cancer cell. However, a tumour consists of more than cancer cells. A major part of all solid tumours is made up by the stroma. The tumour stroma is defined as the non-malignant cells of a tumour such as fibroblasts, the cells of the vascular and immune systems as well as the extracellular matrix (ECM). The basement membrane (BM) is a specialized form of the ECM in which type IV collagen is the major protein component. All epithelial cells need a contact to the BM and the definition of an invasive cancer is the degradation of the BM and the spread of cancer cells beyond this structure. Different metastatic growth patterns of CLM have previously been described, namely the desmoplastic, pushing and replacement type of CLM. These differ in their stromal reaction in the border, which separates the tumour from the normal liver. In this thesis the tumour stroma of CRC and CLM is studied with a special emphasis on stromal collagens. The aim is to investigate whether stromal collagens/ circulating type IV collagen can be used as tumour markers for CRC and CLM, and to compare this to the conventional marker CEA. The circulating type IV collagen level is also measured in liver metastases from other primary tumours than CRC. Furthermore, the differences between the stroma of a primary CRC that metastasizes to the liver when compared to a CRC that never spreads are analysed. Additionally, the metastatic growth pattern of CLM is studied in relation to the primary tumour, stromal components and survival. We also sought out to find whether CRC cell lines possess the trait to produce ECM proteins endogenously, and in response to a normal liver stroma in a novel organotypic model for CLM.Methods: Expression patterns of type I, III and IV collagen were studied by immunofluorescence (IF), chemical staining and immunohistochemistry (IHC) in normal colorectal tissue, normal liver, CRC, CLM, benign liver lesions and in liver metastases of other origin than CRC. Circulating plasma levels of type IV collagen were analysed in healthy controls, patients with CRC (T stage I-III) and in patients with CLM. Samples were analysed at the time of diagnosis, during and after oncological and surgical treatment and at the time of relapsing or progressive disease. Additionally, circulating levels were analysed in patients with benign liver lesions and in liver metastases of other origin than CRC. The metastatic growth pattern of CLM was classified according to earlier descriptions. CRC cell lines were studied regarding their production of type IV collagen. The growth, invasiveness and stromal production in CRC cell lines were also investigated in a new organotypic model for CLM using human liver specimens.Results: Circulating type IV collagen levels are increased in patients with CLM and other epithelial-derived liver metastases, and is found normal in patients with primary CRC (stage I-III), with liver metastases from tumours of non-epithelial origin, benign liver lesions and in healthy controls. The type IV collagen levels in patients with CLM reflect the tumour burden in the liver, decreases in response to therapy and is found increased in progressive or relapsing disease. The combination of circulating type IV collagen and CEA increased the sensitivity and specificity for detecting CLM. Livermetastatic CRC displayed an increased stromal production when compared to non-metastatic CRC, with an increased type IV collagen expression in the direct vicinity of the CRC cells. The earlier described growth patterns of CLM were verified, with the pushing type of CLM associated with a short survival and poor outcome. Furthermore, CRC cell lines possess the trait of endogenously producing type IV collagen. The novel organotypic liver model revealed that CRC cell lines grown in the context of normal liver stroma, devoid of other cells, does not elicit a desmoplastic reaction.Conclusion: Circulating type IV collagen is a promising tumour marker for CLM, where the levels reflect the hepatic tumour burden and can detect disease relapse after liver surgery. The combination of the tumour markers CEA and type IV collagen is superior to CEA alone. The stromal composition of primary CRC predicts the risk of subsequent CLM and the metastatic growth pattern of CLM is related to survival.