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BACKGROUND

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Prevalence

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Anal cancer accounts for 3% of all lower gastrointestinal tract malignancies in the United States.1 It is predicted that 8080 new cases of anal cancer will be diagnosed in the United States in 2016, with this the disease will account for 1080 deaths.1 Of the estimated cases of anal cancer in 2016, 5160 cases will occur among women and 2920 among men, a 1.7-fold higher number of cases among women.1 Squamous cell carcinomas (SCC) comprise the overwhelming majority of anal tumors although other rare histologic subtypes include adenocarcinoma, melanoma, neuroendocrine, and sarcoma.2 In this chapter, the term anal cancer will refer to anal canal SCC, unless otherwise specified. Anal cancer is classified as a human papillomavirus (HPV)-associated cancer and accounts for 15.6% of all new HPV-associated cancers diagnosed annually.3

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The incidence of anal cancer has increased significantly in the past 30 years, jumping 160% in men and 78% in women4,5 (Fig. 116-1). When examined by gender and race, white females (2.6 per 100,000) and black males (2.1 per 100,000) have the highest annual incidence rates and Asian/Pacific Islander men and women (0.3 per 100,000 and 0.5 per 100,000, respectively) have the lowest.3 The incidence of anal cancer also increases with age. The age-adjusted Surveillance, Epidemiology, and End Results (SEER) incidence rates in 2010 were 1.1 per 100,000 and 5.8 per 100,000 for those diagnosed before the age of 65, and 65 or older, respectively.6

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FIGURE 116-1

Trends in the number of new anal cancer cases and deaths per 100,000 people from 1975 to 2010 using SEER data.

Graphic Jump Location
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Survival

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The overall 5-year survival rate for anal cancer is 65.6%;6 however, this varies considerably by stage at diagnosis (79.6% for local disease; 59.8% for regional disease, and 31.3% for distant disease at diagnosis).6 The age-adjusted death rate for patients with cancer of the anus, anal canal, and anorectum is approximately 0.2 per 100,000 per year6 with an average age at death of 66 years old.7

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Anatomy

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The anus represents the distal-most portion of the gastrointestinal tract and consists of a glandular mucosa-lined anal canal and an epidermis-lined anal margin. It is helpful to divide the anal canal by anatomic landmarks to allow for more precise localization of lesions and treatment planning. The surgical anal canal is defined as extending from the anorectal ring (a palpable landmark representing the upper level of the anal sphincter complex) to the anal verge8 (Fig. 116-2). The mucosa of the proximal anal canal is of endodermal origin and has lymphatic drainage to the perirectal (mesorectal and superior rectal) and internal iliac (hypogastric) nodes. The mucosa of the distal anal canal is of ectodermal ...

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