Role of microsatellite instability in predicting lymph node metastasis in early colorectal cancer

Abstract

Background: Surgical resection is the main treatment for early colorectal cancer because of the chance of regional lymph node metastasis. The risk of lymph node metastasis depends on pathological staging. However, even with risk factors of lymph node metastasis, more than 70% of patients who undergo surgical resection for early colorectal cancer appear not to have regional lymph node metastasis. Colorectal cancers with high-frequency microsatellite instability (MSI-H) are reported to have decreased likelihood of metastasis to either regional lymph nodes or distant organs. The aim of this study is to evaluate microsatellite instability as a predictive factor for regional lymph node metastasis.Patients and Methods: One hundred forty-seven patients with early colorectal cancer who underwent surgical resection from Jan 2011 to May 2011 were enrolled. Genomic DNA was extracted from normal and tumor tissue and amplified by polymerase chain reaction. Five microsatellite markers were used (BAT-25, BAT-26, D2S123, D5S346, and D17S250). Tumors that showed instability at 40% or more were classified as MSI-H, whereas other tumors were classified as low frequency MSI (MSI-L) or no instability (MSS). Results: Among 147 T1 colorectal cancer patients, 24 patients had lymph node metastasis. Histology, lymphovascular involvement, and depth of invasion were statistically significant factors of lymph node metastasis. MSI-high, MSI-low, and MSS colorectal cancers accounted for 7%, 5%, and 88%, respectively, of the 147 T1 colorectal cancer cases. Microsatellite status was not statistically significant in lymph node metastasis. Ten patients with MSI-H had no lymph node metastasis. There was no difference in disease-free survival or overall survival between patients with MSI-H and patients with MSI-L/MSS.Conclusions: In T1 colorectal cancer, histologic grade, presence of lymphvascular invasion, and depth of tumor invasion are the factors associated with lymph node metastasis. Although further investigation is needed, microsatellite instability may be a molecular marker of early colorectal cancer that can help predict regional lymph node metastasis.