The purpose of this study was to establish a standard histological classification for intra-operative histological examination of ductal resection margins in cholangiocarcinoma to distinguish between epithelial and intramural lesions and to clarify correlations between the new classification and clinical outcomes. Intra-operative diagnosis of ductal margins was performed for 357 stumps from 216 patients undergoing surgical resection of cholangiocarcinoma at the National Cancer Center, Japan. Three expert pathologists reviewed the materials and established a histological classification defined by grade of atypia. The new classification comprised four categories: 'insufficient', insufficient for diagnosis due to distortion of specimen; 'negative for malignancy', no atypia suggestive of neoplasia; 'undetermined lesion', specimen showing either cellular or structural atypia; and 'positive for malignancy', specimen showing both cellular and structural atypia. Each category was defined to distinguish between epithelial and intramural lesions. Validity and reproducibility of the proposed classification were found to be moderate to substantial. Multivariate analyses using the clinicopathological factors identified to be associated with overall survival by univariate analyses indicated that patients diagnosed with 'positive for malignancy' in intramural lesions of the proximal margin displayed significant poor prognosis. Meanwhile, in patients diagnosed with 'positive for malignancy' or 'undetermined lesion' in epithelial lesions of the proximal margin, no difference in overall survival was apparent compared to patients diagnosed with 'negative for malignancy'. We propose new histological classification for intra-operative histological examination of ductal resection margins in cholangiocarcinoma that shows a correlation with patients' prognosis and should facilitate the determination of ductal resection margin status for cholangiocarcinoma.
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