S1775 Small Cell Cancer of the Rectum: A Rare Entity

Abstract

INTRODUCTION: Small cell cancer (SmCC) a type of neuroendocrine cancer (NEC) occurs rarely in the rectum. We describe the presentation, diagnosis and outcome following treatment in a patient with rectal SmCC. CASE DESCRIPTION/METHODS: A 70-year-old female presented with 6 weeks of daily post defecatory lower abdominal pain and cramping without bleeding, diarrhea, constipation or weight loss. She had 2 non-rectal tubular adenomas in a colonoscopy 3 years earlier. On exam, abdomen was soft, non-distended and non-tender. Colonoscopy showed a distal rectal mass located posteriorly, starting 1.5 cm proximal to the anal verge and extending to above the surgical-anorectal junction (Figure 1).The mass was hard and fixed with a central cratered appearance occupying 20% of the colonic circumference. Biopsy revealed small carcinoma cells with scant cytoplasm and nuclear irregularity with molding. The tumor cells were positive for pancytokeratin, CK-7, chromogranin, synaptophysin, CD56 and TTF-1;Negative for CK20 and CD45, all of which are consistent with SmCC, a poorly differentiated NEC. Positron emission tomography-Computed tomography (PET-CT) scan showed focal activity in the rectum without lymph node or distant metastasis. She received 4 cycles of cisplatin/etoposide and 2 months of radiation. Sigmoidoscopy with biopsies done 14 months later revealed no rectal mass or disease recurrence (Figure 2). The patient is doing well overall and serial imaging and endoscopic surveillance is planned. DISCUSSION: Despite having the highest number of neuroendocrine cells, GI NEC is unusual (0.6% of GI cancers). Esophagus is the most common site for SmCC ∼ 53% incidence, and rectum the least common ∼ 7%. SmCC clinically presents similar to other colorectal malignancies without any exclusive features. While there is a standardized multimodal approach for rectal adenocarcinoma; there is no recommendation for rectal SmCC. As per National Comprehensive Cancer Network, the management is guided by extrapolating from treatment modalities used for lung SmCC. A combination of surgery, chemotherapy and radiotherapy has been suggested for optimal survival. Although the data regarding prognosis and overall survival following multimodal approach is scant, management in our patient suggests that chemotherapy and radiation alone in non metastatic rectal SmCC may be adequate, but this remains to be shown in larger studies.Figure 1.: Colonoscopy done at diagnosis showing rectal mass at the anorectal junction.Figure 2.: Follow up sigmoidoscopy after treatment without any evidence of a mass.