Via Research Recognition Day 2024 VCOM-Carolinas

Clinical Case-Based Reports

Primary Squamous Cell Carcinoma of the Rectum Kara R. Harris, OMS-IV, Daniel M. Jacques, MD Edward Via College of Osteopathic Medicine - Carolinas, Spartanburg, SC

Discussion

Abstract

Case Presentation

Primary rectal squamous cell carcinoma (SCC) is an extremely rare occurrence. In this report, we describe a case of a 61-year-old female that was found to have a polypoid rectal mass on routine screening colonoscopy. Pathology revealed this to be keratinizing squamous cell carcinoma, and chemotherapy and radiation was initiated. It is our hope that by outlining this unique condition, that we highlight the importance of a broad differential when colonic polyps are discovered.

Criteria have been established to formally diagnose SCC of the rectum: a primary squamous cancer from a distant site must be excluded, the lesion must not be associated with a squamous cell lined fistula, the mass must not be an extension of a distal anal SCC, and the lesion must be confirmed to be SCC on histology (2). Our diagnostic algorithm attempted to meet all these requirements. On colonoscope examination, the mass did not appear to grow distally past the dentate line. The polypoid lesion was biopsied using hot snare during colonoscopy and histologically confirmed to be keratinizing squamous cell carcinoma. The patient underwent full-body PET scan to determine that there was not an underlying primary squamous tumor, which would make the mass in question a distant metastasis. There was no evidence for an associated fistulizing process. Our specimen was deemed to be HPV p16 positive, which leads us to question the pathologic process of our patient’s carcinoma. While it is more commonly thought to relate to strictly anal SCC, HPV has been shown to be associated with columnar mucosa and preexisting adenomas within the colon (9). There is also evidence that the virus can induce squamous metaplasia in cultured adenocarcinoma cells via an E6-7 fusion protein (10). Therefore, we cannot conclude with certainty that this is a case of anal SCC. Further investigation into the role of HPV in colorectal squamous cell carcinomas is needed. Conclusions This case report highlights the importance of developing a wide differential for colorectal lesions because, although it is uncommon, these may be pathologic variants of squamous cell carcinoma. We discussed a case of a 61-year-old female who presented asymptomatically with a keratinizing squamous cell carcinoma of the rectum. It will be imperative for future studies that diagnostic criteria be met to delineate the true incidence of this cancer.

Introduction

Figure 1. Procedural photos of polypoid terminal rectal mass.

Colorectal cancer (CRC) is a broad term in that encompasses several pathologic subtypes. The vast majority – over 90% – of these cancers are adenocarcinomas (1). Based on literature review, the documented incidence of rectal squamous cell carcinoma is as low as 0.25 to 0.1 per 1,000 cases of CRC (2). Very few cases have yet to be reported. However, the rectum is reportedly the most common location in the lower gastrointestinal tract for primary squamous cell carcinoma to be discovered (3).The pathogenesis of SCC of the rectum is mostly unknown. There have been studies looking into the possibility that high-risk strains of human papillomavirus (HPV) may be implicated given its role in the development of anal and cervical cancers (4). Case Presentation 61-year-old female presented for routine screening colonoscopy. She had no acute complaints at the time of presentation. She denied any abdominal pain, rectal pain, melena, hematochezia, changes in bowel habits, changes in urinary habits. Her family history is notable for a sister with diagnosis of rectal cancer. The patient’s previous colonoscopy in 2017 was significant only for a 4 mm hyperplastic polyp in the sigmoid colon. She was recommended to follow up for repeat colonoscopy in 5 years due to her family history of CRC. Colonoscopic exam revealed a 2 mm tubular adenoma in the proximal ascending colon. A mass with polypoid component was then noted in the terminal rectum that extended ~2cm distally. No obvious external anal masses or lesions were visualized. Upon inspection, the polyp appeared to be a solely rectal mass consistent with rectal carcinoma. The area was marked with tattoo, and appropriate biopsies were obtained and sent to pathology. Analysis revealed a keratinizing squamous cell carcinoma that extended to the inked resection margin. Differential diagnoses at this point included primary squamous cell carcinoma versus metastatic process. Staging was carried out via non-contrast pelvic MRI and full-body PET scan. Biopsy specimen also underwent human papillomavirus (HPV) testing. She was sent for consultation appointments with both medical and radiation oncology.

Non-contrast pelvic MRI revealed a 2.4 x 2.1 rectal mass that was estimated to be 3 cm from the anal verge, possibly involving the anterior aspect of the internal anal sphincter. MRI also highlights 3 suspicious mesorectal lymph nodes. Subsequent PET scan showed focal activity in the most distal rectum that was consistent with the known mass. It did not show any clear evidence for metastatic disease, including the previously noted lymph nodes.

Figure 2 . Sagittal view (left) and axial view (right) of pelvic MRI demonstrating low rectal mass Immunohistochemical staining results of the biopsy specimen were positive for p16 which is consistent with involvement by high-risk HPV. Given this new finding, and the behavior of the tumor, it was decided by her medical oncology team that this lesion would be treated similarly to a primary anal SCC with chemotherapy and pelvic radiation. Follow up exams will be carried out at intervals determined by her oncologic team. Discussion Due to the rare nature of rectal SCC, the risk factors, presentation, treatment protocol, survival statistics, and pathogenesis are quite difficult to establish. There have been several case reports and documentation of colorectal SCC metastasizing to the lung, bone, brain, and skin, with extremely poor patient outcomes (7). In our case, the patient had been recalled for a 5 year follow up colonoscopy due to her family history of CRC which almost certainly prevented further invasion of the tumor since she was asymptomatic at presentation.

References

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2024 Research Recognition Day