Anal cancer (staging)

Anal cancer staging refers to the TNM classification of anal cancer published by the American Joint Committee on Cancer (AJCC). The most recent version of the AJCC staging system for anal cancer, version 9, was published in 2022 with a required use date of 1 January 2023 ³.

Primary tumour (T)

• TX: primary tumour cannot be assessed

• T0: no evidence of primary tumour

• Tis: carcinoma in situ (Bowen disease, high-grade squamous intraepithelial lesion [HSIL], anal intraepithelial neoplasia II-III (AIN II-III)

• T1: tumour 2 cm or less in greatest dimension

• T2: tumour >2 cm but <5 cm in greatest dimension

• T3: tumour >5 cm in greatest dimension

• T4: tumour of any size invades adjacent organ(s), e.g. vagina, urethra, bladder

  • note that direct invasion of the rectal wall, perirectal skin, subcutaneous tissue, or the sphincter muscle(s) is not classified as T4

The tumour size can be measured on any of the planes and must reflect its longest diameter. 

Regional lymph nodes (N)

• Nx: regional lymph nodes cannot be assessed

• N0: no regional lymph node metastasis

• N1: metastasis in regional lymph nodes

  • N1a: metastases in inguinal, mesorectal, and/or internal iliac lymph nodes

  • N1b: metastases in external iliac lymph nodes

  • N1c: metastases in external iliac and N1a nodes (inguinal, mesorectal, and/or internal iliac lymph nodes)

Size criteria for anal carcinoma have not yet been validated, and MRI morphologic features are usually more helpful in defining nodal involvement: irregular contours/spiculated margins and heterogeneity or necrosis. F-18 FDG PET-CT has higher sensitivity (89-93%) than MRI and CT (~62%) in determining nodal involvement ^ref. 

Distant metastasis (M)

• Mx: distant metastasis cannot be assessed

• M0: no distant metastasis

• M1: distant metastasis

Involvement of para-aortic or more distant lymph nodes is considered as M1. Besides para-aortic nodes, the liver and lungs are the other common sites for metastasis ^ref.