An inconspicuous fallopian-tube carcinoma clinically manifested as a rectovaginal septal tumor: a pitfall for diagnosis and treatment.

We report an unusual metastasis of an inconspicuous fallopian-tube carcinoma to the rectovaginal septum in a 67-year-old woman. The 4-cm tumor of serous adenocarcinoma was identified in the rectovaginal space with intact vaginal and rectal mucosa. The patient underwent an abdominoperineal resection with adjacent rectum and the bilateral uterine annexes, which were macroscopically intact. Unexpectedly, invasive and intraepithelial serous adenocarcinoma in fallopian-tube fimbria was microscopically observed, suggesting that the fallopian fimbria was the origin of the rectovaginal septum tumor. The clonality of these two tumors was confirmed by the presence of an identical single nucleotide point mutation in TP53. The patient received six cycles of adjuvant paclitaxel and carboplatin combination chemotherapy. There was no sign of recurrence after 17 months of treatment. This case study demonstrates that the fallopian-tube carcinoma, which exhibited minimal growth in the primary site, has the potential to metastasize to the retroperitoneal space and suggests that the fallopian-tube fimbria must be closely examined in cases of adenocarcinoma of unknown origin.