Adenosquamous Cell Carcinoma of the Colon

Abstract

Purpose: A 36-year-old woman with ulcerative colitis (UC) had a total proctocolectomy for differentiated adenocarcinoma (T1N0M0) three years prior to the current presentation of three months of epigastric pain with radiation to her back. Examination revealed epigastric fullness without a palpable mass. CEA was 7 ng/mL (nl:0-3ng/mL) and CA19-9 was 1022 units/mL (nl:<37units/mL). Two solid pancreatic masses were identified on CT. EUS-FNA samples of the body and the neck of the pancreas were positive for squamous cell carcinoma (SCC). Immunohistochemical staining revealed that the tumor was strongly positive for p16. In situ hybridization for HPV was negative. Given the rarity of primary pancreatic SCC slides from the patient's previous proctocolectomy were reviewed. Similar to the pancreatic tumor, the colonic tumor was p16 positive, HR-HPV negative and had foci suggestive of squamous differentiation. The pathology was felt to be most consistent with pancreatic metastasis from a colon primary, rather than a de novo lesion. Conclusion: Pure SCC in the pancreas is a metastatic lesion until proven otherwise. One of the most common sites of primary tumors metastatic to the pancreas is the colon. Despite the prevalence of adenocarcinoma of the colon; combined, pure SCC and mixed adenosquamous (Ad-SCC) account for 0.1% of colon cancers. However, in patients with UC the relative incidence is reported to be 1.7%. The squamous component of Ad-SCC metastasizes more frequently and is more aggressive than the glandular counterpart. While the mechanism that gives rise to Ad-SCC of the colon is not well understood, basal cells proliferation as a response to mucosal injury, squamous metaplasia of glandular epithelium as a response to chronic inflammation and squamous differentiation of adenomas or adenocarcinomas, are possible explanations. The rarity of colorectal Ad-SCC and SCC complicates establishment of accurate prognosis and makes treatment selection difficult, Miyamoto, et al. believe that surgical resection is a better first line approach. Adjuvant treatment may be considered if the patient has a good performance status. Both Ad-SCC and SCC of the colon are rare tumors. Several published reports suggest an increased incidence in patients with UC. However, Cheng, et al. have questioned whether irritable bowel disease (IBD) is an etiological factor or if the increased numbers of SCC identified in patients with IBD is due to a selection bias; as these patients have surveillance colonoscopy more frequently than the average population. At present, any evidence based conclusions regarding etiology or treatment of pancreatic SCC, colonic SCC and Ad-SCC remain elusive.