Invasive cancer arising in a colonic inverted hyperplastic polyp.

py for the investigation of lower abdominal pain. Colonoscopy showed a whitish, flat, elevated polyp, 10mm in diameter, in the ascending colon (l" Fig. 1). Endoscopic mucosal resection (EMR) was carried out, and the resected specimen histologically revealed both invasive cancer and serrated adenomatous glands coexisting in an inverted hyperplastic polyp (IHP) (l" Fig. 2a–c). A follow-up colonoscopy 6 months later revealed an irregularly elevated normal mucosa with fold convergence adjacent to the EMR scar (l" Fig. 3). Although endoscopic features suggested a recurrent cancer, endoscopic biopsies unfortunately failed to identify recurrent cancer histologically. Surprisingly, a second follow-up colonoscopy only 3 months later showed an advanced colon cancer (l" Fig. 4). Endoscopic biopsies showed poorly differentiated adenocarcinoma, and therefore surgical resection was carried out. Histologically, the recurrent cancer was a subserosally invasive, poorly differentiated adenocarcinoma with vascular invasion and nodal involvement, and it was classified as stage III (T3N2M0). This IHP was 10mm in diameter, which is a so-called large hyperplastic polyp, and interestingly it demonstrated a characteristic endoscopic and histologic feature of IHP [1]. IHP is a variant form of hyperplastic polyp with a characteristic histologic feature of epithelial misplacement or inversion of the epithelium into the submucosa [2]. Our case was unique and the histology detected the presence of not only an invasive, poorly differentiated carcinoma but also serrated adenomatous glands surrounded by hyperplastic glands. To date, three cases of IHP associated with adenoma have been reported [3]; however this is the first case report of both of invasive cancer and serrated adenoma arising in an IHP. Recently, serrated polyps have been histologically defined as polyps that demonstrate a serrated or “sawtoothed” appearance, and include hyperplastic polyps, serrated adenoma, and Invasive cancer arising in a colonic inverted hyperplastic polyp