AB052. SOH25_AB_140. Deep infiltrating endometriosis or locally advanced rectal cancer?—a diagnostic dilemma

Background: Endometriosis is a common disease in females defined as the presence of endometrial-like tissue outside the uterine cavity. Deep infiltrating endometriosis (DIE) often affects the pouch of Douglas and muscle wall of the colon and rectum. Locally advanced rectal cancer (LARC) is a complex entity which requires multidisciplinary care with the widely accepted treatment strategy of neoadjuvant treatment followed by total mesorectal excision (TME). Methods: We report the case of a 50-year-old female with significant history of DIE invading the upper rectum. She presented for an outpatient endoscopy and a polypoidal lesion at the site of known DIE was suspicious for a primary rectal neoplasm. Magnetic resonance imaging (MRI) was suggestive of LARC of the upper rectum. Thorough multidisciplinary team (MDT) discussion to discern DIE from LARC was undertaken. Results: The patient underwent an anterior resection with en bloc total abdominal hysterectomy and bilateral salpingo-oophorectomy with covering loop ileostomy. She had an uncomplicated postoperative recovery. Postoperative histology demonstrated pT2pNibpMxR0. She proceeded to standard adjuvant chemotherapy for colorectal adenocarcinoma i.e., 6 cycles of FOLFOX (folinic acid + fluorouracil + oxaliplatin). Conclusions: We rely on imaging to establish the great majority of tumour features for therapeutic decision making in LARC. MRI is the pillar of multidisciplinary discussion for this pathology. Our case highlights how normal variant anatomy such as DIE in an age group increasingly affected by LARC can present challenges in therapeutic decision making. In the setting of progressive Total Neoadjuvant Therapy for LARC, the need for robust MDT discussions around patient selection and preoperative staging is demonstrated for best cancer care.