Immunohistochemical and molecular features of primary clear cell-adenocarcinoma of the rectum, as predictive factors for individualized therapy.

An 82-year-old male was hospitalized with rectal carcinoma that was confirmed endoscopically. Surgical resection of the rectum was performed. Intraoperative examination showed a solitary hepatic metastasis; metastasectomy was also performed. Histological examination of the surgical specimen showed mainly a trabecular arrangement of the tumor cells, alternating with tubuloglandular areas, the tumor being diagnosed in stage IV. The high-power-view examination showed that the tumor cells presented clear cytoplasm, and were diffusely marked by AE1/AE3 keratin, carcinoembryonic antigen (CEA), and CD10. A focal immunostain was also observed for keratins 7/20, vascular endothelial growth factor (VEGF), and its receptor (VEGF-R2). The tumor was proved to be microsatellite stable, presenting K-ras mutation. Based on the immunoprofile and computer scanning, metastases from clear cell renal cell carcinoma and adrenocortical carcinoma have been excluded. Based on these characteristics and the tumor stage, the final diagnosis was primary clear cell adenocarcinoma (CCA). Bevacizumab-based antiangiogenic therapy was indicated. This is the 12th primary CCA of the colorectum ever reported, and the first from Eastern Europe.