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MSI High and Low

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Last Modified: January 24, 2012

Question

What does MSI high/low mean? Which has a better prognosis in colon cancer?

Answer

Carolyn Vachani, RN, MSN, AOCN, OncoLink Nurse Educator, responds:

Tumors are identified as MSI-H (i.e. MSI-high), meaning they are MMR deficient (dMMR), or MSI-stable and MSI-low, meaning they are considered MMR proficient (pMMR). Studies have found MSI-H tumors are associated with a better prognosis and is present in approximately 22% of stage II colon tumors (but only 12% of stage III tumors). Several studies have found that patients with stage II MSI-H tumors not only did not derive any benefit from 5-FU adjuvant therapy, but they actually fared worse if they were treated. This was not seen for stage III MSI-H tumors. MS-stable disease, however, may benefit from 5-FU based treatment. Some experts recommend testing for MSI testing as another tool to determine the need for treatment in stage II disease.

Learn more: http://www.oncolink.org/types/article.cfm?c=5&s=11&ss=84&id=9621

This question and answer was part of the OncoLink Brown Bag Chat Series. View the entire Interpreting Test Results transcript.