Anal Cancer

KEY FEATURES

• Carcinoma of the anus is relatively rare: only 2% of all gastrointestinal malignancies

• Occurred in ∼ 9440 patients in the United States in 2022

• More commonly seen in women than in men (2:1 ratio)

• Squamous cell carcinomas (SCC) make up the majority of anal cancers; adenocarcinomas account for the remainder

• > 90% of anal cancers are associated with human papillomavirus (HPV) infection (most commonly, HPV-16 and HPV-18)

• Increased incidence among

  • Women with HPV-associated cervical, vulvar, or vaginal squamous intraepithelial lesions or cancer

  • Men who have sex with men

  • Women and men who are HIV-positive or have received a solid organ transplant

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 (< 2 cm) superficial lesions of the perianal skin

• Combined-modality therapy for SCC of the anal canal as well as large perianal tumors invading the sphincter or rectum: external radiation plus simultaneous chemotherapy (5-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

• Treatment of anal adenocarcinoma is like that of rectal adenocarcinoma with trimodality therapy: chemoradiotherapy, chemotherapy, and abdominoperineal resection

• Surveillance includes

  • Digital rectal exam

  • Anoscopy

  • Inguinal lymph node palpation every 3–6 months for 5 years

  • CT scans of the chest, abdomen, and pelvis annually for 3 years

• 5-year survival rate

  • 81% for localized tumors

  • ∼ 30% for metastatic disease