Uncommon Case of Primary Squamous Cell Carcinoma of the Rectum

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Primary squamous cell cancer (SCC) of the rectum is a rare malignancy of the gastrointestinal tract, making up only 0.1-0.25% of all colorectal carcinomas. Due to its rare incidence, the pathophysiology has not been well described in literature. Here, we report a case of a patient who presented with rectal pain and was ultimately diagnosed with SCC of the rectum. This is a 61-year-old female who initially presented with diarrhea, rectal pain, and weight loss. Colonoscopy was performed but the colonoscope was unable to traverse beyond 8 cm due to a near-fully obstructing circumferential mass. MRI pelvis revealed a partially obstructing rectal mass measuring 7.4 cm, located 6.4 cm above the anorectal junction. Biopsies revealed squamous cell carcinoma undermining rectal mucosa with lymphatic invasion. The immunohistochemical stain was positive for p16 suggesting a HPV-mediated process. Patient underwent a laparoscopic diverting loop sigmoid colostomy due to the obstructing mass and was then recommended to undergo chemoradiation. First described in 1933, most cases of rectal SCC have reported similar presentations to colorectal adenocarcinoma including rectal pain, bleeding and changes in bowel habits. Rectal SCC has been linked to inflammatory bowel conditions such as ulcerative colitis due to proliferation of squamous metaplasia after damage to colonic mucosa. Other cases have found associations to high risk HPV, radiation, HIV, schistosomiasis and amebiasis as inciting etiology. Biopsy of the tumor can yield a definitive diagnosis. Histologically, tumor cells in SCC can be positive for CK 5/6, p40, and p63, and HPV-related carcinomas can be positive for p16. Although similar in presentation to adenocarcinoma of the rectum, SCC has a different epidemiology, etiology, and pathogenesis, thus requiring a different therapeutic approach which includes chemoradiation.1604_A Figure 1. Circumferential obstructing mass in the rectosigmoid colon1604_B Figure 2. T2 weighted MRI axial view. Exophytic solid mass measuring 7.4 cm located 1-5 o'clock of the rectum with extensive involvement of mesolectal fascia involvement bilaterally1604_C Figure 3. Microscopically, the tumor consisted of large, atypical, squamous epithelial cells (A) (H&E, x20). Tumor cells were large with bright eosinophilic, focally glassy cytoplasm and vesicular nuclei with small to medium sized nucleoli (B) (H&E, x40). Immunohistochemically tumor cells were diffusely positive for p40 (C) and showed over expression of p16 (D)