Undifferentiated cancer with unknown primary location infiltrating the rectum – a case report

Abstract

Colorectal cancer (CRC) is the third leading malignancy in men after prostate and lung cancer. Adenocarcinomas account for about 90% of all colorectal cancer cases. Carcinomas of unknown primary site (CUPs) are usually found in patients > 60 years of age. They account for 3% of all malignancies in Poland. We describe a diagnostically challenging case of undifferentiated carcinoma of unknown primary site invading the rectum. Rectal specimens collected during endoscopy and open biopsy, as well as samples collected during laparotomy from the side of the peritoneal cavity did not confirm cancer despite progressing clinical symptoms of an ongoing neoplastic process. Histopathological diagnosis was obtained only with core-needle biopsy of the rectal infiltration and sphincter muscles. The histopathological confirmation of carcinoma invading the sigmoid colon, rectum, anus and the mesorectum described in PET-CT enabled patient qualification for further palliative treatment.