A case of low-grade intestinal-type mucinous neoplasm of the fallopian tube with KRAS exon 2 mutation.

Several types of mucinous lesions of the fallopian tube have been reported, including metaplastic and neoplastic lesions, most of which exhibit gastric phenotypes. Here, we report a unique case of a mucinous tumor arising in the right fallopian tube of a 36-year-old female who presented with refractory abdominal pain for approximately one year. Abdominal CT and MRI found a cystic lesion leading to the diagnosis of hematosalpinx, thus right salpingo-oophorectomy and appendectomy were performed. Macroscopic findings included cystic dilatation of the distal portion of the right fallopian tube, filled with gelatinous mucin. Histologically, mucinous columnar cells proliferated in papillary configurations in the cystic region without invasion, resembling low-grade appendiceal mucinous neoplasms. Immunohistochemical analysis revealed that the neoplastic cells expressed CDX-2 and SATB2, but not WT-1, PAX8, ER, PgR, or claudin 18. Sanger sequencing of the mucinous lesion identified a KRAS exon 2 mutation (p.G12A), confirming similar pathologic and genetic characteristics to ovarian mucinous borderline tumors. This rare low grade intestinal-type mucinous tumor indicates the fallopian tube epithelium can give rise to tumors resembling low-grade appendiceal mucinous neoplasms and cause pseudomyxoma peritonei without appendiceal lesions.