Objective:

To assess the prevalence of deficient mismatch repair (dMMR) protein deficiency and its relation to clinicopathological characteristics in Chinese colorectal cancer (CRC) patients.

Approach:

Key Findings:

• 18 out of 80 patients (22.5%) were identified as dMMR.
• The most common deficiency pattern was isolated PMS2 loss (50.0% of dMMR cases).
• dMMR CRCs were significantly more likely to be located in the right colon (61.1% vs. 22.6%, P < 0.001).
• dMMR CRCs were more likely to be poorly differentiated (50.0% vs. 19.4%, P = 0.009) and exhibit mucinous adenocarcinoma (27.8% vs. 6.5%, P = 0.014).
• dMMR status was linked to a lower rate of lymph node metastasis (22.2% vs. 46.8%, P = 0.052).

Interpretation:

The prevalence of dMMR in this cohort was 22.5%. dMMR CRCs display a distinct clinicopathological profile characterized by right-sided location, poor differentiation, mucinous histology, larger tumor size, and a lower likelihood of lymph node metastasis.

Limitations:

• Findings regarding isolated MSH6 loss and its association with younger age and poor differentiation are preliminary due to the small number of cases.

Conclusion:

Routine IHC-based MMR testing in CRC patients is supported, but confirmatory molecular testing is necessary to differentiate sporadic from Lynch syndrome-associated dMMR cases.

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