الفهرس 
Anatomy of the colorectum
Epidemiology of colorectal carcinomaOnly 14 pages are availabe for public view
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Abstract
Colorectal carcinoma ranks the third most common type of
cancer and constitutes a major contributor to cancer morbidity and
mortality globally. In Egypt, colorectal cancer is not uncommon;
representing the 6th most frequent cancer among both sexes
combined. It is a heterogeneous disease with diverse histological and
biological features, clinical presentations, behavior and response to
therapy.
The molecular pathogenesis of CRC has been recently
evolved and CRC is increasingly classified into specific phenotypes
based on different carcinogenetic pathways. Most colorectal
carcinomas arise through a conventional adenoma-carcinoma
sequence. Along the adenoma-carcinoma sequence, colorectal
tumorigenesis can progress through either chromosomal instability
pathway with multiple alterations in chromosome number,
chromosomal rearrangements, or gene amplifications or the
microsatellite instability pathway. Microsatellite instability (MSI) is
a hypermutable phenotype caused by defects in DNA mismatch
repair due to the inactivation of one of the four mismatch repair
genes: MSH2, MLH1, MSH6, and PMS2.
MSI is equivalent to the loss of staining by
immunohistochemistry (IHC) of one of the mismatch repair genes;
most frequently MSH2 and MLH1, since both signify an abnormality
in mismatch repair. It became apparent that a subset of early onset
CRC is characterized by a large number of mutations at MS
sequences; 3% of these are associated with Lynch syndrome and the /