A RARE CASE OF PRIMARY SUB-MUCOSAL RECTAL SQUAMOUS CELL CARCINOMA DIAGNOSED WITH ENDOSCOPIC ULTRASOUND

Background: A squamous cell carcinoma (SCC) of the rectum is a rare primary colorectal malignancy. Here we report a case of primary submucosal SCC of the rectum treated with chemo-radiation. Case Report/Results: A 56- year-old female with no significant past medical history presented with complaints of generalized abdominal discomfort with onset few weeks ago. Computed tomography (CT) of abdomen and pelvis with intravenous contrast showed soft tissue mass measuring around 20 mm at the left lateral wall of the rectum. Patient underwent colonoscopy and rectal ultrasound showing two hypoechoic lesions (largest of size 16-17 mm and smaller lesion around 10 mm) at around 10 cm from the anal verge. Both lesions were in close proximity and appeared to be originating from the muscularis propria layer. Fine needle aspiration was performed separately from both lesions with pathology consistent with squamous cell carcinoma. No significant perirectal or iliac lymphadenopathy was noticed on rectal ultrasound. Positron emission tomography (PET)/CT scan showed hyper-metabolic rectal lesion consistent with known malignancy with additional foci of hyper-metabolism in the perirectal fat concerning for nodal disease without distant metastases (T2 N1 M0). The patient underwent chemotherapy (mitomycin-C with 5-fluorouracil) and radiation therapy. Surveillance PET-CT showed no residual lesions in rectal wall. Conclusion: Primary rectal SCC is a distinct and extremely rare form of colorectal malignancy making the presentation of sub-mucosal rectal SCC an even rarer entity. Etiopathogenesis of rectal SCC is poorly understood. An important step in diagnosis is the exclusion of other primary SCC with metastasis to gastrointestinal tract. Endoscopic ultrasound and PET-CT provide important diagnostic information to plan for further management. There has been a shift in preference towards definitive chemo-radiation for rectal SCC, simulating anal canal SCC standard of care. Due to the paucity of literature the treatment plan at this time should be individualized based on the presentation of the patient.