Objective: An important cause of liver re-metastasis from colon cancer is remnant micrometastasis (MiM). MiM is a miniscule metastatic lesion that results from hematogenous spread of tumor cells along with or after the original metastasis from colon to liver. Thus, an adequate surgical margin is necessary to lower a patient's risk of relapse. Questions have arisen whether the guideline 1-cm surgical margin can be reduced in cases in which neoadjuvant chemotherapy (NAC) has been performed. We

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... ducted a histopathologic study to determine the appropriate hepatectomy margin in such cases. Methods: We studied 76 cases of colorectal liver metastasis treated between January 2005 and December 2013 at St. Marianna University School of Medicine Hospital. NAC had been performed in 35 of these cases. We evaluated patients' sex; age; site, clinical stage, and histologic type of the primary tumor, clinical and histologic effects of the NAC, histologic characteristics and size of the hepatic macrometastasis, number of cases in which MiM was found and the number of MiMs per case, histologic characteristics and size of the MiM(s), distance from the macrometastasis to the MiM, and exact location of the MiM(s) and tested between-group differences in these variables statistically. We also tested correlation between size of the macrometastasis and both distance between the macrometastasis and MiM and the number of MiMs per case. Results: Positive, but non-significant, correlation was found between size of the macrometastasis and both distance between the macrometastasis and MiM and the number of MiMs per case. Regardless of whether NAC was performed, most MiMs we examined were within 5 mm of the macrometastasis, but some were within 9 mm. Conclusion: Our data indicate that, regardless of whether NAC is performed before hepatectomy for liver metastasis from colorectal cancer, a minimum 1-cm surgical margin is necessary to ensure inclusion of micrometastases.