Significance of molecular genetic alterations and apoptosis in colorectal cancer

• Colorectal cancer is a serious health problem in Western societies. In Sweden it is the second most common malignancy among females, and the third in males, and the third leading cause of cancer related death in both sexes. To date it is known that several biological pathways can lead to colorectal cancer. An enhanced understanding of the molecular and cellular events occurring within these pathways should ultimately result in better tailored preventive, diagnostic and therapeutic approaches. An important goal is to identify cancer predisposing genetic variants that would make genetic screening of at-risk individuals possible, and to find parametres which could define homogenous subgroups associated with a certain prognosis.Impaired apoptotic processes have been implicated in colorectal tumourigenesis. In order to explore the significance of apoptosis in relation to proliferative activity, and other clinicopatological data including prognosis, apoptotic rates were measured by TUNEL in 158 colorectal tumours. A significant increase of apoptotic rate was observed with advancing tumour stage, from Dukes' A to D. Apoptotic rates were further significantly associated with the proliferative activity in the tumour, indicated by the proliferating cell nuclear antigen (PCNA). Thus it seems that apoptotic levels in the tumour might reflect tumour progression, and further that the processes of apoptosis and proliferation are coupled. Apoptosis was not related to p53, bcl-2 or K-ras, and did not confer any additional prognostic information.APC has been referred to as a "gatekeeper" in the progression of colorectal cancer. It is in a key position to regulate the balance between cell adhesion and migration and may also be involved in proliferation and apoptosis. The two germ line APC variants I1307K and E1317Q have been associated with increased colorectal cancer risk in certain populations, but have yet never been investigated in Swedish colorectal cancer patients. We screened J 94 colorectal cancer patients with and without a family history of colorectal cancer by DNA sequencing analysis, but did not find any of the variants. We conclude that I1307K and E1317Q are rare or absent in this population and should not confer any increased colorectal cancer risk in the Swedish population.The microsatellite instability pathway accounts for the majority of tumours in hereditary non-polyposis colorectal cancer (HNPCC) patients and about 15% of sporadic colorectal cancer cases. Inactivated mismatch repair (MMR) genes leads to an increased mutation rate, especially within repetitive DNA sequencies called microsatellites which are prone to replication errors, a phenomenon referred to as microsatellite instability (MSI). Several genes with microsatellites within their coding regions are targeted by MSI, and are possibly involved in tumourigenesis, including the repair gene MBD4 which is involved in maintaining the integrity of genomic methylation patterns. We aimed to determine the microsatellite status of 201 colorectal tumours using the marker Bat 26 in order to evaluate the relationship of MSI and clinicopathological variables including survival. We further aimed to investigate whether MBD4 is a MSI target gene in colorectal cancer, and to search for mutational associations with clinicopathological factors to reveal eventual phenotypical effects. Surprisingly, MSI was not associated with survival, as opposed to many previous studies, suggesting that the prognostic significance and the factors associated with it demands further investigation. MBD4 seemed to be a target of MSI, since the mutations were restricted only to MSI tumours. The clinicopathological variables associated with the MBD4 mutated tumours were likely the reflection of MSI features aquired prior to the MBD4 mutation, including right colon location and mucinous histology. The significance of these mutations remains to be determined in a largermaterial.

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