Anal Cancer

Key Features

• Carcinoma of the anus is relatively rare: only 1–2% of all cancers of the large intestine and anus

• Squamous cancers (keratinizing, transitional cell, and cloacogenic), 80%; adenocarcinomas, 20%

• Increased incidence among

  • People practicing receptive anal intercourse

  • Those with a history of anorectal warts

  • Those with HIV infection

• Human papillomavirus (HPV) infection in > 80%

• Increased risk in combined HIV and HPV infection

Clinical Findings

• Anal bleeding

• Pain

• Local mass

• The lesion is often confused with hemorrhoids or other common anal disorders

• Tumors tend to become annular, invade the sphincter, and spread upward via the lymphatics into the perirectal mesenteric lymphatic nodes

Diagnosis

• CT or MRI scans of the abdomen and pelvis are required to identify regional lymphadenopathy or metastatic disease at diagnosis

• PET imaging may be used in conjunction

Treatment

• Wide local excision for small (< 3 cm) superficial lesions of the perianal skin

• Combined-modality therapy for tumors invading the sphincter or rectum: external radiation with simultaneous chemotherapy (fluorouracil plus mitomycin)

• Local control achieved in approximately 80% of patients

• Radical surgery (abdominoperineal resection) for patients in whom chemotherapy and radiation therapy fail

• Metastatic disease is generally treated with carboplatin and paclitaxel

• Checkpoint inhibitor therapy with either nivolumab or pembrolizumab has been shown in small studies to result in disease control in up to 46% of patients with chemotherapy-refractory, metastatic or unresectable disease

• 5-year survival rate

  • 81% for localized (stages I–III) disease

  • ~30% for metastatic (stage IV) disease

• In a large controlled trial, HPV vaccination of healthy men (16–26 years old) who have sex with men decreased the incidence of anal intraepithelial neoplasia by 50%