S4112 Rectal Squamous Cell Carcinoma: A Rare Case of Malignant Small Polyp

Introduction: Rectal squamous cell carcinoma (RSCC) is a rare type of rectal cancer with an estimated incidence of 0.10 to 0.25 per 1000 colorectal cancers. Squamous cell carcinoma usually affects the anal canal due to presence of columnar, stratified columnar and stratified squamous cells when rectal histology is primarily composed of simple columnar epithelial cells driving the common incidence of rectal adenocarcinoma. In this article we describe a rare case of RSCC. Case Description/Methods: A 75-year-old woman with a past medical history of hypertension, Alzheimer’s dementia, peripheral artery disease, hypercholesterolemia, Vitamin B12 and Vitamin D deficiency presented to the clinic for surveillance colonoscopy with a prior history of a 10 mm hyperplastic transverse colon polyp that was removed. On this visit, the patient reports a 20-pound weight loss in the past year. She denies any family history of gastrointestinal malignancies or high-risk polyps. Patient was hemodynamically stable with an unremarkable physical exam. Labs show a hemoglobin: 11.9 g/dl, hematocrit: 36%, WBC: 5.1 U/L, platelets: 229000 U/L, iron: 131, total iron binding capacity: 300 MCG/DL, ferritin: 25 NG/ML, CEA: 2.1 NG/ML/L, HIV negative. Colonoscopy showed a 4 mm sessile polyp in the rectum which was removed by a cold snare. Pathology results of rectal biopsy showed neoplastic cells with fragments of squamous cell carcinoma, with basaloid features. Positive for P40, P63, P16, CKpan, CK7, AE1/3 with about 70% Ki-67 and high-risk human papillomavirus. Negative for CD56, chromogranin, synaptophysin, CK20 and CDX2. She then underwent endoscopic ultrasound revealing pT1 N0 M0 stage. Therefore, she underwent endoscopic mucosal resection of a 1 cm lesion with slightly depressed center and elevated margins along the proximal anal verge, negative margins. The patient completed chemoradiation, with present remission status. Discussion: Rarity of RSCC makes providing a definite treatment plan challenging. Cancerous rectal masses are commonly deemed to be adenocarcinoma. Staged using TNM criteria, treatment options commonly include chemoradiation using 5 fluorouracil and mitomycin c, endoscopic mucosal resection/dissection relative to stage and management of human papillomavirus infection. However, criteria for selection has yet to be established in literature due to RSCC’s infrequent occurrence. The histological pattern of the rectum makes the differential of RSCC unanticipated for however it should be taken into consideration as it can be easily missed on routine colonoscopy.