²Epidemiology:
Women demonstrated a far greater risk for anal cancer in patients with ten or more lifetime sexual partners [relative risk (RR)=4.5]; a history of anal warts (RR=11.7), genital warts (RR=4.6), gonorrhea (RR=3.3), cervical dyspasia (RR=2.3), human immunodeficiency virus (RR=1.7), a known history of a sexually transmitted disease in sexual partners (RR=2.4), or engaging in anal receptive intercourse before the age of 30 (RR=3.4) or multiple partners (RR=2.5), Human papillomavirus (HPV-16).1
Etiology:
The cause of anal cancer is unknown.2
Signs & Symptoms:
Bleeding and anal discomfort, awareness of an anal mass, pruritus, anL discharge and less frequently pain, alteration in bowel habits, gross fecal incontinence resulting from sphincter destruction, fecal soiling is common.1
Diagnostic Procedures:
H&P, Proctoscopy, Biopsy, Fine needle aspiration biopsy, chest x-ray, CT of abdomen and pelvis, liver and renal chemistry, CBC, colonoscopy, and air contrast barium enema.³
Histology:
Squamous cell carcinoma subdivided into large cell keratinizing, large cell nonkeratinizing, and basaloid. Other types are mucoepidermoid, adenocarcinoma, small cell, and undifferentiated cancers.³
Lymph Node Drainage:
There are 3 main lymph node systems; perianal skin, anal verge, and canal distal. These drain to the superficial inguinal nodes, femoral nodes, and to the external iliac system. A intramural system connects the lymph nodes the anal nodes to the lymph nodes of the rectum.³
Metastatic Spread:
Anal canal tumors usually spread locally and normally invade the perianal tissues, sphincter muscle and invade the local tissues.⁴ Anal margin lesions are normally treated as skin cancers versus anal canal tumors that are treated as regular tumors.⁵ Metastatic spread is normally through the lympahtic system and occurs relatively early.⁶ Distant metstatic disease with squamous cell cancer is possible with the main sites being: liver, lungs, extrapelvic lymph nodes and peritonuem.⁷
Grading:
General grading system recommended by the American Joint Committee on Cancer and the International Union Against Cancer is based on the degree of cell differentiation:
Grade 1: low grade, cells well-differentiated.
Grade 2: moderate grade, cells moderately differentiated.
Grade 3: high grade, cells undifferentiated.
There is also a classification of that the grade can't be assessed.⁸

Staging:
The major staging system for stomach cancer is the American Joint Committee on Cancer TNM system⁹
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Radiation Side Effects:

Side effects of radiation therapy vary based on the area of the body treated and the dose of radiation given. Skin changes (like a sunburn) are common and improve after radiation is stopped. Temporary anal irritation and pain with discomfort during bowel movements may also occur. Other possible side effects include fatigue, nausea, or diarrhea. Long-term side effects can also occur. Damage to anal tissue by radiation may cause scar tissue to form. This scar tissue can sometimes keep the anal sphincter from working as it should. Radiation to the pelvis can weaken the bones, increasing the risk of fractures of the pelvis or hip. Radiation can also damage blood vessels that nourish the lining of the rectum and lead to chronic radiation proctitis (inflammation of the lining of the rectum). This can cause rectal bleeding.
Prognosis:
anatomic extent of disease provides the most prognosic value. when anal cancer is confined to the pelvis, size ofthe primary tumor is the most usseful indicator for local control, preservation of anorectal function, and survival.¹⁰
Treatments:
The 3 main methods of treatment for anal cancer are surgery, radiation therapy, and chemotherapy. Often the best approach combines 2 or more of these strategies. In the past, surgery was the only treatment that could cure anal cancer, but now most anal cancers are treated with radiation and chemotherapy combined (called chemoradiation or chemoradiotherapy). This approach often eliminates the need for surgery.
Most use a four fields or AP/PA pelvic field approach including a boost to the tumor bed with a perineal electron field or another multifield technique. The pelvic filed extends from the lumbosacral -sacroiliac region to 3 cm distal to the lowest extent of the tumor. The inferior border typically flashes the perineum. The lateral border may extend to include treatment of the inguinal lymph nodes on the AP field only, placing that field edge at the midlateral aspect of the femoral heads. The PA field is kept narrower because the anteriorly located inguinal nodes do not receive much contribution from the posterior field. This also avoids and excessive dose to the femoral heads. The dose regimen used with radiation alone is 6000 cGy to the primary. This dose is reduced to approximately 4500-5040 cGy if chemotherapy is used. Field reduction are implemented after a dose of 4500cGy to reduce small bowel toxicity
TD5/5:
Organ (1/3), (2/3), (3/3)
Small bowel 50 Gy, xx, 40 Gy
Colon 55 Gy, xx, 45 Gy
Rectum 75 Gy, 65 Gy, 60 Gy¹²


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Figure 1: Conventional AP/PA anal fields with DRR from Eclipse¹³


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Figure 2: Field setup for conventional anal treatment, including inguinal
nodes¹²

References

1. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002.
2. Philip Rubin, Clinical Oncology-A Multidisciplinary Approach for Physicians and Students. 7th edition, Philadelphia, PA: W. B. Saunders Co.; 1993.

3. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002.
4.Gunderson LL, Haddock MG, Goldberg, R, et. al. Alimentary Cancer. In: Rubin P, ed. Clinical Oncology: A Multidisciplinary Approach for Physicians and Students. 8th ed.Philadelphia, PA: W.B. Saunders Company; 2001:748.

5.Gunderson LL, Haddock MG, Goldberg, R, et. al. Alimentary Cancer. In: Rubin P, ed. Clinical Oncology: A Multidisciplinary Approach for Physicians and Students. 8th ed.Philadelphia, PA: W.B. Saunders Company; 2001:748.
6. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002:407-408.

7. Cummings BJ. Metastatic anal cancer: the search for the cure. Onkologie. 2006;29:5-6.
8. Spitalnik PF, di Sant'agnese PA. The Pathology of cancer. In: Rubin P, ed. Clinical Oncology: A Multidisciplinary Approach for Physicians and Students. 8th ed.Philadelphia, PA: W.B. Saunders Company; 2001:54.
9. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002:410.

10. Chao KS, Perez CA, Brady LW. Radiation Oncology- Management Decisions. 2nd ed.
Philadelphia, PA: Lippincott, Williams & Wilkins; 2002
11. Anal Cancer questions at
:
www.acs.org/analcancer
12. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins. 2002.
13. United Hospital. Eclipse planning system. Accessed January 21, 2010.