[Amputation neuroma with a difficult differential diagnosis from perihilar cholangiocarcinoma:a case report].

Biliary amputation neuroma is a rare benign tumor that develops due to the peribiliary dissection of nerve fibers during cholecystectomy, a common bile duct surgery, or lymph node dissection performed in gastric cancer surgery. We report a case of amputation neuroma that presented a challenging differential diagnosis from perihilar cholangiocarcinoma. A 64-year-old man, who had undergone open cholecystectomy 30 years ago, was incidentally found to have a bile duct tumor during computed tomography (CT) following surgery for renal cell carcinoma. He had no specific symptoms, and blood test results showed only a slight elevation in alkaline phosphatase levels. Contrast-enhanced CT revealed a 10-mm solid tumor with contrast effect in the common bile duct. On cholangiography, the tumor appeared as a protruding lesion with a smooth surface unilaterally. Given the atypical findings suggestive of cholangiocarcinoma, three bile duct biopsies were performed. Pathological examination did not rule out adenocarcinoma. The patient opted for surgery;however, an intraoperative rapid histological examination confirmed a benign disease, thereby avoiding extensive surgery. Consequently, a minimally invasive bile duct resection was performed. Postoperative histopathological examination revealed the tumor to be an amputation neuroma. Biliary amputation neuromas are characterized as unilateral protruding lesions with contrast effect or benign strictures. If such findings are observed in a patient with a history of surgery around the bile duct, the possibility of an amputation neuroma should be considered. However, completely ruling out malignancy preoperatively, even when suspecting amputation neuroma, can be challenging;therefore, considering surgery to achieve a definitive diagnosis is reasonable. During surgery, a rapid intraoperative histological examination is useful to avoid extensive procedures. In conclusion, diagnosing an amputation neuroma before surgery can be difficult, as it can mimic malignant tumors such as bile duct cancers. In this case, although a preoperative diagnosis of amputation neuroma was not feasible, performing a rapid intraoperative pathological examination helped avoid extensive surgery.

Movements of Ancient Human Endogenous Retroviruses Detected in SOX2-Expressing Cells.

Human endogenous retroviruses (HERVs) occupy approximately 8% of the human genome. HERVs, transcribed in early embryos, are epigenetically silenced in somatic cells, except under pathological conditions. HERV-K is thought to protect embryos from exogenous viral infection. However, uncontrolled HERV-K expression in somatic cells has been implicated in several diseases. Here, we show that SOX2, which plays a key role in maintaining the pluripotency of stem cells, is critical for HERV-K LTR5Hs. HERV-K undergoes retrotransposition within producer cells in the absence of Env expression. Furthermore, we identified new HERV-K integration sites in long-term culture of induced pluripotent stem cells that express SOX2. These results suggest that the strict dependence of HERV-K on SOX2 has allowed HERV-K to protect early embryos during evolution while limiting the potentially harmful effects of HERV-K retrotransposition on host genome integrity in these early embryos. IMPORTANCE Human endogenous retroviruses (HERVs) account for approximately 8% of the human genome; however, the physiological role of HERV-K remains unknown. This study found that HERV-K LTR5Hs and LTR5B were transactivated by SOX2, which is essential for maintaining and reestablishing pluripotency. HERV-K can undergo retrotransposition within producer cells without env expression, and new integration sites may affect cell proliferation. In induced pluripotent stem cells (iPSCs), genomic impairment due to HERV-K retrotransposition has been identified, but it is a rare event. Considering the retention of SOX2-responsive elements in the HERV-K long terminal repeat (LTR) for over 20 million years, we conclude that HERV-K may play important physiological roles in SOX2-expressing cells.