From the Guidelines
Anorectal cancer staging should be performed using the TNM staging system, which evaluates the tumor (T), lymph node involvement (N), and metastasis (M), as recommended by the most recent guidelines 1. The TNM staging system for anal canal cancer is detailed in the guidelines, with an emphasis on the primary tumor size determined through direct examination and microscopic confirmation 1.
- The T stage is determined by the size of the primary tumor, with T1 indicating tumor invasion into the submucosa, and higher stages indicating more extensive invasion.
- Lymph node staging ranges from N0 (no regional lymph node metastasis) to N1c (metastasis in external iliac with any N1a nodes), with N1a representing metastasis in inguinal, mesorectal, superior rectal, internal iliac, or obturator nodes, and N1b representing metastasis in external iliac nodes 1.
- M0 indicates no distant metastasis, while M1 confirms distant spread. The prognosis of anal carcinoma is related to the primary tumor size and presence of lymph node metastases, with 5-year survival rates ranging from 80% for patients with localized disease to 30.5% for those with distant metastasis 1.
- Comprehensive staging requires multiple imaging modalities, including direct examination, microscopic confirmation, and imaging studies such as CT or PET scans for distant metastasis detection.
- Accurate staging is essential because it determines whether patients receive neoadjuvant therapy, the type of treatment approach needed, and whether adjuvant therapy is warranted. The most recent guidelines should be followed for anorectal cancer staging, as they provide the most up-to-date and evidence-based recommendations for staging and treatment 1.
From the Research
Anorectal Cancer Staging
- Anorectal cancer staging is a critical process that affects treatment approaches, with different staging systems used for anal and rectal cancers 2, 3.
- For anal cancer, primary staging and assessment after chemoradiation therapy are commonly performed using MRI, which is considered the preferred imaging modality 2, 4.
- CT and PET/CT are useful in evaluating lymph node metastases and distant metastatic disease in both anal and rectal cancers 2, 3.
Imaging Modalities
- MRI is the preferred imaging modality for local-regional staging of anal cancer, while CT is used for evaluation of metastatic disease 2, 4.
- For rectal cancer, MRI plays a key role in pre- and posttreatment evaluation, assisting in tailoring the most appropriate treatment option 5, 6.
- MRI helps in characterizing the main anatomic structures and their relationship with the tumor, providing information on T and N categories, and detecting extramural vascular invasion and involvement of surrounding structures 5.
Staging Distinctions
- Staging of nonmetastatic rectal cancers is dependent on the depth of invasion (T stage) and the number of involved regional lymph nodes (N stage) 3.
- Staging of nonmetastatic anal cancers is determined according to the size of the primary mass and the combination of regional nodal sites involved, without considering the number of positive nodes at each site 3.
- The radiologist must recognize and report critical anatomic and staging distinctions, which affect the use of radiation therapy in patients with anal and rectal cancers 3.