Genome-wide differences between microsatellite stable and unstable colorectal tumors

Area of Science:

• Oncology
• Genetics
• Genomics

Background:

• Genomic copy number changes are common in cancers and drive carcinogenesis.
• Microsatellite instability (MSI) colorectal tumors are generally considered genetically stable and diploid.
• This study investigates copy number alterations in both MSS and MSI colorectal tumors.

Purpose of the Study:

• To compare copy number alterations and gene-expression profiles between MSS and MSI colorectal tumors.
• To identify specific genomic regions altered in each tumor type.
• To correlate copy number changes with gene expression patterns.

Main Methods:

• Comparative genomic hybridization (CGH) including metaphase CGH (mCGH) and array-CGH.
• Gene expression profiling.
• Analysis of fresh-frozen primary colorectal tumors and cell lines.

Main Results:

• MSS tumors showed specific deletions at 1p22, 4q26, and 15q21, and gains at +20, +8q, -8p, and -18q.
• MSI tumors exhibited gains at 22q13.
• Array-CGH identified common alterations like gains at 8q24, 16q24.3, 20q13, and loss of 5q21 in both tumor types.
• Gene expression analysis linked specific genes to copy number changes in corresponding genomic regions.

Conclusions:

• Colorectal cancer is a heterogeneous disease with diverse genomic profiles.
• Copy number changes are not exclusive to MSS colorectal tumors, indicating genomic instability can occur in both MSS and MSI phenotypes.
• The findings highlight the biological significance of copy number changes in colorectal tumorigenesis.