Background: Invasion of submucosa (ISM) is required for the pathological diagnosis of colorectal cancer according to the WHO criteria. A large proportion of colorectal cancers may be underdiagnosed as high-grade intraepithelial neoplasia (HGIN) because ISM is not identified in the preoperative biopsy. The aim of this study was to investigate the clinicopathologic features that are associated with missing the diagnosis of ISM in biopsy specimens of invasive colorectal cancer.
Methods: Three hundred and sixteen patients diagnosed with colorectal cancer between January 2007 and December 2008 with well-preserved preoperative biopsy specimens were enrolled in the study. Three hundred and eleven patients had an isolated lesion, and five had two lesions. Biopsy specimens were reevaluated by two senior pathologists. Clinicopathologic features, biopsy pathology and surgical pathology results of all patients were analyzed by univariate and multivariate analyses.
Results: ISM was identified in 216 cases (67.3 %) by biopsy-based pathological examination, and missed in 105 (32.7 %) cases, 72 of which were diagnosed as HGIN. Univariate analysis indicated that in colorectal cancer patients with smaller biopsy specimens (P = 0.042), mucinous or signet-ring cell carcinoma (P = 0.003), higher WHO tumor grade (P = 0.001) and positive lymph nodes (P = 0.011), ISM was more likely to be missed. There was a trend toward an increased diagnosis of ISM with the increase in the number of biopsy specimens (P = 0.105). On multivariate logistic regression analysis, smaller biopsy specimens (OR, 1.810; 95 % CI, 1.081-3.032; P = 0.024) and higher WHO tumor grade (OR, 2.073; 95 % CI, 1.046-4.107; P = 0.037) were the only factors associated with failure to identify ISM.
Conclusions: A large number of invasive colorectal cancers are at risk of being underdiagnosed as HGIN by biopsy-based pathology. The smaller the biopsy size, the less likely it is that the muscularis mucosae is included in the specimen. Also, in the more advanced or aggressive colorectal cancers, ISM is more likely to be missed on biopsy, which may be due to the destruction of the muscularis mucosae by more aggressive cancers.