Inaccurate and incomplete diagnoses of malignant polyps as a cause of pathologic tumor stage T0 colectomy

The purpose of this study was to retrospectively review cases of pathologic tumor stage T0 (pT0) colectomy for colon cancer to determine whether any cases could be attributed to inaccurate (false-positive) or incomplete biopsy diagnoses. We conducted a search of our laboratory archives for all biopsy diagnoses of invasive colonic adenocarcinoma over a period of 11 years. Rectal carcinomas and those treated neoadjuvantly were excluded. The subset of interest consisted of those biopsies that were followed up by a colectomy specimen with no invasive malignancy. There were 762 biopsy diagnoses of invasive colon cancer, of which 564 (74.0%) had subsequent colectomy. Thirty-two resection cases (5.7%) were classified as pT0 on resection. After review, 2 gastrointestinal pathologists determined that 4 (0.7%) of the original biopsies represented false-positive diagnoses of invasive malignancy. They agreed that 24 cases represented malignant polyps containing invasive adenocarcinoma and disagreed on the presence of invasion in 4 cases. Less than half (15/32, 46.9%) of reviewed cases had included all parameters required, when diagnosing early colon cancer in a polypectomy. We are not aware of any other published quality assurance studies looking specifically at false diagnosis of invasion as a cause of pT0 colon cancer resections. In this retrospective review, most biopsy diagnoses were accurate. However, false-positive biopsy diagnoses of colon cancer do occur and may lead to pT0 colectomy.