The anal canal extends from the rectum to the perianal skin and is lined by a mucous membrane that covers the internal sphincter. The following is a staging system for anal cAnal Cancer that has been described by the American Joint Committee on Cancer (AJCC) and the International Union Against Cancer.[1] Tumors of the anal margin (below the anal verge and involving the perianal hair-bearing skin) are classified with skin tumors.

TNM Definitions

Primary tumor (T)

• TX: Primary tumor cannot be assessed
• T0: No evidence of primary tumor
• Tis: Carcinoma in situ
• T1: Tumor 2 cm or less in greatest dimension
• T2: Tumor more than 2 cm but not more than 5 cm in greatest dimension
• T3: Tumor more than 5 cm in greatest dimension
• T4: Tumor of any size that invades adjacent organ(s), e.g., vagina, urethra, bladder*

*Direct invasion of the rectal wall, perirectal skin, subcutaneous tissue, or the sphincter muscle(s) is not classified as T4.

Regional lymph nodes (N)

• NX: Regional lymph nodes cannot be assessed
• N0: No regional lymph node metastasis
• N1: Metastasis in perirectal lymph node(s)
• N2: Metastasis in unilateral internal iliac and/or inguinal lymph node(s)
• N3: Metastasis in perirectal and inguinal lymph nodes and/or bilateral internal iliac and/or inguinal lymph nodes

Distant metastasis (M)

• MX: Distant metastasis cannot be assessed
• M0: No distant metastasis
• M1: Distant metastasis

AJCC Stage Groupings

Stage 0

• Tis, N0, M0

Stage I

• T1, N0, M0

Stage II

• T2, N0, M0
• T3, N0, M0

Stage IIIA

• T1, N1, M0
• T2, N1, M0
• T3, N1, M0
• T4, N0, M0

Stage IIIB

• T4, N1, M0
• Any T, N2, M0
• Any T, N3, M0

Stage IV

• Any T, any N, M1

References:

1. Anal canal. In: American Joint Committee on Cancer.: AJCC Cancer Staging Manual. 6th ed. New York, NY: Springer, 2002, pp 125-130.