eP350 - A Rare Case of Squamous Cell Carcinoma of the Rectum

Purpose/Background: Squamous cell carcinoma of the rectum is a rare entity, representing only one in 300 rectal cancers. Primary squamous cell carcinomas of the lower gastrointestinal tract usually occur in the anus and are primarily linked to human papillomavirus (HPV) infection. There are only 73 cases of primary rectal squamous cell malignancies documented in the literature. Basaloid squamous cell carcinomas are an especially rare variant. Here, we present the unusual case of a basaloid squamous cell carcinoma of the rectum.Methods/Interventions: A 57-year-old female underwent a colonoscopy for evaluation of progressive obstructive symptoms and hematochezia. Biopsies of a rectal mass were obtained. HPV serotyping was performed. Subsequent workup included magnetic resonance imaging (MRI) of the pelvis, computed tomography (CT) scan, positron emission tomography (PET) scan, and testing for sexually transmitted diseases.Results/Outcomes: Colonoscopy revealed a large, circumferential, and near-completely obstructing ulcerated mass of the distal rectum, 4.5cm proximal to the anal verge (Figure 1). Cold forceps biopsies revealed poorly differentiated squamous cell carcinoma with basaloid features (Figure 2). The tumor was positive for p40, p63, and CK (cytokeratin) 5, immunohistochemical markers consistent with squamous differentiation (Figure 3). It was diffusely positive for p16, and further testing revealed high-risk HPV types 16 and 18. MRI showed T4 disease with extension through the wall of the rectum to the pelvic sidewalls and coccyx (Figure 4). CT scan of the chest, abdomen, and pelvis and PET scan were without evidence of metastatic disease. Serologic testing for human immunodeficiency virus (HIV), syphilis, and hepatitis B and C were negative. In a setting of symptomatic near-obstruction, the patient underwent fecal diversion with a laparoscopic loop sigmoid colostomy. She recovered well from surgery and was referred to a high-volume rectal cancer center for further treatment of her rare malignancy.Conclusion/

Discussion: Squamous cell carcinoma of the rectum is very rare, comprising 0.3% of all rectal cancers. The cause is thought to be chronic inflammation leading to squamous metaplasia. Associated factors include HPV, HIV, chronic enteric infections, ulcerative colitis, and radiation. Our patient had a history of HPV disease of her cervix requiring previous excision, with no other known risk factors. Given its rarity, the optimal treatment for rectal squamous cell carcinoma is not well established. Similar to anal squamous cell cancers, chemoradiation therapy remains the treatment of choice, with surgical resection reserved for salvage of persistent or recurrent disease. Our patient has just completed chemoradiation treatment. She did well, and her outcome is to be determined."Figure 1.

Colonoscopic view of the rectal mass.
Figure 2.

Poorly differentiated squamous cell carcinoma, consisting of pleomorphic hyperchromatic nuclei with basaloid features and brisk mitoses.
Figure 3.

Immunohistochemical stains positive for: p40 (top), p63 (middle), and CK5 (bottom).
Figure 4.

MRI view (sagittal plane) of the rectal mass."