eP208 - Abdominoperineal Resection for Monophasic Synovial Sarcoma Arising from the Rectum

Purpose/Background: Synovial sarcoma, a malignant mesenchymal neoplasm, often occurs in the extremities. Rarely does it arise from the digestive tract. If it does, the highest incidence would be in the upper gastrointestinal tract. Of the 68 cases documented worldwide, only two were found in the rectum. This reports a case of a 60-year-old man diagnosed with monophasic synovial sarcoma of the low rectum.Methods/Interventions: The patient presented with constipation that was associated with hematochezia and anal pain. No changes in stool caliber, or weight loss, was reported. While being worked up for hemorrhoidal disease at a local hospital, a rectal mass was discovered on proctoscopy. The surgeon, unfortunately, proceeded with hemorrhoidectomy and biopsy of the tumor. Histopathology eventually revealed: spindle cell neoplasm. He was advised transfer to a tertiary institution for further work-up and definitive management. On digital rectal examination, there was a palpable firm, broad-based tumor at the anal verge, with tenderness precluding further examination.Pelvic MRI showed an irregular wall thickening of the anorectum, with a maximum thickness of 2.1 cm, and length of 9 cm. The posterior margin of the prostate gland was adherent to the mass, and an involvement of the external sphincter was seen at the left anterior area. Contrast-enhanced computed tomography (CT) scan of the chest and abdomen revealed no distant metastasis.Results/Outcomes: After discussion in a multidisciplinary team (MDT) meeting, the decision to proceed with surgical resection was made since the patient had been experiencing severe anal pain intractable to pain medications due to tumor infiltration. He underwent an abdominoperineal resection (APR) with en bloc prostatectomy. (Fig 1A) Intraoperatively, a friable, fungating rectal tumor at the verge adherent to the prostate was noted. No enlarged nodes nor findings of metastatic spread were seen. On gross examination by the pathologist, there was a 5.5 × 4.5 × 1.8 cm cream white, rubbery, centrally ulcerated tumor with serpiginous borders. Microscopic examination revealed a malignant spindle cell neoplasm. Immunohistochemistry (IHC) studies were later to confirm the diagnosis of a monophasic synovial sarcoma as supported by TLE1 positivity and SOX10 negativity. (Fig 1B)Given this diagnosis, no adjuvant therapy was recommended as there is lack of evidence on response to chemotherapy, or radiotherapy. The patient was advised on postoperative surveillance. At eight months postoperatively, no recurrence or distant metastases were noted.Conclusion/

Discussion: In cases of rectal masses, appropriate work-up should complement history taking and physical examination. Endoscopy with biopsy, pelvic MRI, and CT scan of the chest and abdomen should be requested to ascertain the character and status of the disease. Synovial sarcoma of the gastrointestinal tract is uncommon, hence the decision to proceed with either outright surgery or neoadjuvant treatment is upon the discretion of an MDT.Based on literature, patients older than 25 years, with tumor size more than 5 cm, and poorly differentiated histology are considered high-risk, thus adjuvant therapy should be considered. In addition, closer monitoring and surveillance is warranted. Treatment of such rare entities remains to be a challenge hence reporting is of utmost importance to further understand their behavior and treatment options that may result in better patient outcomes.Figure 1(A) Gross specimen of the sigmoid colon and rectum with the prostate gland. (B) H&E 40x: spindle-shaped tumor cells with hyperchromatic, ovoid to irregularly-shaped, vesicular nuclei, with evenly dispersed chromatin. Pancytokeratin 40x: positive; focal cytoplasmic staining in neoplastic cells. TLE1 40x: positive; weak to moderate nuclear staining in 50-60% of cells. SOX10 40x: negative for staining in cells of interest. (PGH, 2023)