Cancer of the Anal Canal
Summary of Key Points
Staging Evaluation
• American Joint Commission on Cancer (AJCC) tumor–node–metastasis (TNM) staging system for anal cancer is a clinical staging system. Notably, the T stage is based on tumor size rather than depth of invasion as it is in other gastrointestinal cancers.
• Physical examination, evaluating the size, location, mobility, and inguinal nodal involvement, is critical in staging patients and for a baseline comparison to determine response.
• Computed tomography, sigmoidoscopy, endoanal ultrasound, and magnetic resonance imaging or positron emission tomography imaging are helpful in evaluation of the extent of the primary lesion, presence of regional nodal disease or distant metastatic disease.
Primary Therapy
• Primary therapy for anal squamous cell carcinomas consists of definitive chemoradiation with concurrent 5-flourouracil, mitomycin-C, and radiotherapy.
• Surgical resection is only used as salvage for patients who have persistent or recurrent disease after chemoradiation.
• Induction chemotherapy, radiation dose-intensification, and maintenance chemotherapy have not been shown to improve outcomes over standard chemoradiation for anal cancer.
Prognosis
• The outcomes for anal squamous cell carcinoma are good, with a colostomy-free survival of 72% and overall survival of 78% at 5 years with pelvic radiotherapy and concurrent 5-fluorouracil and mitomycin-C.
• More advanced tumors are associated with a higher risk of local recurrence and distant failure.
1. Which of the following statements is true regarding screening and prevention for squamous cell carcinomas of the anal canal:
A Routine annual anal Pap smears are recommended to reduce the risk of anal canal cancer in HIV-positive men.
B HPV vaccination is recommended for girls and boys at age 11 or 12 years and for girls ages 13 to 26 years who have not been previously vaccinated.
C HPV16 is found more frequently in anal carcinomas than in cervical carcinomas, making the quadrivalent vaccine ineffective.
D Because anal intraepithelial neoplasia (AIN) is difficult to detect, high-risk individuals cannot be screened for precursors of invasive anal cancer.
2. For anal squamous cell carcinoma, randomized trials have shown a benefit from all of the following except:
A 5-FU+mitomycin–based chemoradiotherapy versus radiation therapy alone.
B 5-FU+mitomycin–based chemoradiotherapy versus 5-FU–based chemoradiotherapy alone.
C 5-FU+mitomycin–based chemoradiotherapy versus neoadjuvant cisplatin-based chemotherapy alone followed by cisplatin-based chemoradiotherapy.
D IMRT-based chemoradiotherapy versus 3D-planned chemoradiotherapy.
3. For a T3N0M0 squamous cell carcinoma of the anal canal, what is the elective nodal coverage in your radiation field design?
1. Answer: B. The Advisory Committee on Immunization Practices (ACIP) of the Centers of Disease Control (CDC) has recommended human papilloma (HPV) vaccination for preteen girls since 2007 and for preteen boys since 2010 with the goal of reducing HPV infection and, subsequently, the incidence of invasive cervical and anal cancers. More information regarding the HPV vaccine can be found at the CDC website: http://www.cdc.gov/vaccines/vpd-vac/hpv/#recs.
2. Answer: D. There have been no randomized studies evaluating the use of IMRT for anal cancer. There is a phase II single-arm study that establishes the benefit of IMRT in reducing toxicity for anal cancer. There have been randomized studies demonstrating the benefit of concurrent chemotherapy (UKCCCR and EORTC trials), as well as the benefit of mitomycin-C (RTOG 8704). The neoadjuvant cisplatin-based approach was evaluated in the RTOG 98-11 study and found to be associated with worse outcomes.
3. Answer: C. All of these lymph node regions are draining regional nodes for anal canal tumors and therefore should be included in the clinical target volume. For further details on the recommendations for the clinical target volume for anal cancer, please see the RTOG Anorectal Consensus Atlas. (Myerson RJ, Garofalo MC, El Naqa I, et al. Elective clinical target volumes for conformal therapy in anorectal cancer: a Radiation Therapy Oncology Group consensus panel contouring atlas. Int J Radiat Oncol Biol Phys 2009;74:824–30.)
