Serous tubal intraepithelial carcinoma in a suspected heterotopic pregnancy: A rare case report

Primary carcinoma of the fallopian tube continues to be a diagnostic challenge because of its non- specific clinical presentation and rarity. It is usually misdiagnosed or diagnosed only after the specimen was submitted for histopathologic examination. Serous Tubal Intraepithelial Carcinoma (STIC) is considered an early-stage cancerous lesion of the fallopian tube, in most cases, at the fimbriated end.¹ Although it is still controversial, current studies site that the secretory epithelial cells of the fallopian tubes are considered as the main origin of High-grade Serous Carcinoma (HGSC) while the ovarian surface epithelial cells are considered to be the minor origin only.² The etiology of STIC is believed to be associated with BRCA 1/2 mutations with the incidence being 0.6% to 0.7% in women who are carriers of BRCA genes or women with strong family history of breast or ovarian carcinoma.³

This is a case of STIC, initially diagnosed as a case of heterotopic pregnancy in a 34-year-old multigravida who presented with 7 weeks amenorrhea, vaginal bleeding, and acute hypogastric pain with passage of meaty tissues. On internal examination, cervix was open with placental tissues plugging the internal cervical os, uterus was slightly enlarged, no cervical motion tenderness, no adnexal tenderness nor mass palpated. Pregnancy test was positive, and a transvaginal scan showed a right adnexal complex mass suggestive of an evolving unruptured tubal pregnancy measuring 1.05 x 1.90 x 1.42 cm. Patient underwent completion curettage and right salpingectomy. The histopathology report revealed decidual tissues and STIC respectively. Subsequently, patient underwent exploratory laparotomy, peritoneal fluid cytology, total hysterectomy, left salpingectomy and bilateral oophorectomy under spinal anesthesia. Final histopathology examination revealed negative for residual tumor, indicating early detection of the fallopian tube malignancy and therefore good prognosis and survival. This is the first reported case of intrauterine pregnancy – STIC association. Information regarding isolated STIC is rare, however there are systematic review of literature concluding that the rate of HGSC after an isolated STIC diagnosis was 7.1% with a successive incidence of 10.5% after five years and 21.6% after ten years.⁴ Given these data, it is imperative to diagnose and treat isolated cases of STIC to prevent progression to HGSC and to address the other carcinomas that can co- exist with STIC.