Metachronous adenocarcinoma of the anal canal after anterior resection for sporadic primary rectal adenocarcinoma: A rare case report

INTRODUCTION: Anal canal adenocarcinoma is an extremely rare malignancy with poorly defined diagnostic and treatment criteria. PRESENTATION OF CASE: A 42-year-old women was diagnosed with primary anal canal adenocarcinoma 11 months after undergoing anterior resection for primary sporadic rectal adeocarcinoma. Transanal excision was performed and additional adjuvant chemotherapy was given. Immunohistology showed positivity for cytokeratin (CK) 20 and CDX2, and negative CK7, which is compatible with colorectal subtype anal adenocarcinoma. At 6 months follow-up the patient has no evidence of recurrent or metastatic disease. DISCUSSION: Diagnosis of primary anal adenocarcinoma is typically delayed because of its rarity, and vague clinical presentation. Exact histologic criteria remain poorly defined but the use of immunohistology has improved the overall diagnostic accuracy of anal adenocarcinoma and it also helps define its correct origin. Reports on the management and outcomes of this cancer consist mainly of retrospective studies with no consistent treatment strategy and limited comparison data. Most authors currently recommend neoadjuvant chemoradiotherapy and radical resection. Despite aggressive therapy, rates of local failure and distant recurrence remain high. CONCLUSION: Diagnosis of adenocarcinoma of the anal canal is difficult but specific immunohistolgic patterns help to correctly identify its correct origin and subtype. Defining the correct subtype of anal adenocarcinoma may impact treatment strategies of this rare cancer.