An Unusual Case of Human Papillomavirus-Related Anorectal Adenocarcinoma With Progression to Perianal Paget's Disease

Primary adenocarcinoma of the anorectum, compared with squamous cell carcinoma, is a rarer and more aggressive malignant neoplasm. Infection with human papillomavirus (HPV) has been identified as a causal agent in a variety of tumors, including those of the cervix, head and neck, and anogenital region, especially squamous cell carcinoma. However, the relationship between HPV and anorectal adenocarcinoma has not been well studied. In this article, we report an HPV-related anorectal adenocarcinoma arising in a tubulovillous adenoma in a 76 years old female who presented initially with lower gastrointestinal bleeding. The carcinoma cells were positive for cytokeratin 7 and p16 by immunohistochemistry. High-risk HPV RNA in situ hybridization was positive. A follow-up examination of the anal area showed perianal plaques. Histologically, the excision of the perianal lesion showed intraepithelial infiltration by sheets and clusters of large atypical neoplastic cells. The neoplastic cells showed the same immunoprofile compared with the anorectal adenocarcinoma with p16 and high-risk HPV positivity. The findings are consistent with extramammary perianal Paget's disease secondary to anorectal adenocarcinoma. HPV-related adenocarcinoma in the anorectum is a newly recognized entity and was previously considered clinically indolent. Our case uniquely exhibits adenoma-carcinoma-perianal Paget's disease sequence, which has not been reported before. Our findings suggest that evaluation of the patient's lower genital tract for any HPV-associated lesions and long-term follow-up are required to monitor the disease progression in this type of malignancy.