Improved testing for microsatellite instability in colorectal cancer using a simplified 3-marker assay.
BACKGROUND
In colorectal cancer (CRC), microsatellite instability (MSI) is a valuable marker of defective DNA mismatch repair that identifies cancers with distinct phenotypic properties, including favorable survival. However, the optimal assay for MSI status is unknown. We have evaluated a simplified 3-marker assay for MSI and compared it with the 5-marker (NCI) assay to see if technical variations in MSI testing are important.


METHODS
DNA samples from 357 CRCs were evaluated for MSI using the 5 microsatellite markers recommended for the NCI assay (BAT 25, BAT26, D2S123, D5S346, and D17S250). Results were compared with a simplified 3-marker assay (BAT25, BAT26, and D2S123). CRCs identified as MSI were evaluated for their clinical, pathological, and genetic characteristics.


RESULTS
The 5-marker assay identified 96 cancers as MSI. Only 56 of these were MSI by the 3-marker assay (3-marker+ group), leaving 40 cases identified as MSI only by NCI criteria (3-marker- group). The remaining 261 cancers were microsatellite stable (MSS). The 3-marker+ MSI tumors had features characteristic of MSI tumors: more proximal, poorly differentiated, associated with hereditary nonpolyposis colorectal cancer (HNPCC), more BRAF mutations, fewer KRAS mutations, better 5-year disease-specific survival, more frequent mismatch repair (MMR) protein loss, and less likely to be metastatic on presentation (P < .05). Chromosomal arm loss was observed only in 3-marker- MSI and MSS cancers (P < .05).


CONCLUSIONS
The 3-marker MSI assay outperforms the traditional 5-marker assay for identifying patients with favorable prognosis and homogeneous clinical and genetic features. More accurate MSI testing should improve prognostic and predictive scoring systems for colorectal cancer.
Esemuede
Iyare
I
Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, NY, USA. esemuedi@gmail.com
Forslund
Ann
A
Khan
Sajid A
SA
Qin
Li-Xuan
LX
Gimbel
Mark I
MI
Nash
Garrett M
GM
Zeng
Zhaoshi
Z
Rosenberg
Shoshana
S
Shia
Jinru
J
Barany
Francis
F
Paty
Philip B
PB
D000230:Adenocarcinoma / Q000235:genetics* / Q000473:pathology; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001681:Biological Assay; D014408:Biomarkers, Tumor / Q000235:genetics*; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D055028:Comparative Genomic Hybridization; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000235:genetics*; D005260:Female; D005500:Follow-Up Studies; D005820:Genetic Testing; D018095:Germ-Line Mutation / Q000235:genetics*; D006801:Humans; D008207:Lymphatic Metastasis; D008297:Male; D053842:Microsatellite Instability; D018895:Microsatellite Repeats / Q000235:genetics*; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D011379:Prognosis; D011446:Prospective Studies; D015996:Survival Rate; D055815:Young Adult
D014408:Biomarkers, Tumor; D045643:DNA Repair Enzymes