Is fine-needle aspiration (FNA) of inguinal lymph nodes necessary before starting chemoradiation for anal squamous cell carcinoma?

Fine-Needle Aspiration of Inguinal Lymph Nodes Before Starting Chemoradiation for Anal Cancer

Fine-needle aspiration (FNA) of inguinal lymph nodes is not routinely required before starting chemoradiation for anal squamous cell carcinoma, but should be performed when there are enlarged or suspicious nodes on clinical examination or imaging that would alter the radiation treatment plan. 1

Diagnostic Approach to Inguinal Lymph Nodes in Anal Cancer

When FNA is Indicated:

• When inguinal nodes appear suspicious on imaging but do not fulfill definitive criteria for malignancy
• When confirmatory features of malignancy are not evident on either MRI or PET-CT scanning 1
• For clinically palpable inguinal lymph nodes 1
• When characterizing enlarged nodes would alter the radiation therapy plan 1

When FNA is Not Necessary:

• For clinically normal inguinal nodes in patients with early-stage disease
• When nodes already show definitive features of malignancy on imaging (mixed signal intensity or breach of lymph node capsule on MRI) 1

Imaging Assessment Before Considering FNA

The diagnostic workup for inguinal lymph node assessment should follow this sequence:

1. MRI of the pelvis (preferred first-line imaging)

   • Look for mixed signal intensity in nodes
   • Assess for breach of lymph node capsule 1

2. CT scan of thorax, abdomen, and pelvis

   • Required in all patients to assess potential metastatic disease 1

3. PET-CT (optional)

   • Can add value to conventional imaging in initial staging of T2-4 disease
   • Useful to characterize suspicious features seen on MRI
   • Can help confirm nodal involvement when findings are equivocal 1

Important Considerations

Challenges in Nodal Assessment:

• Lymph node assessment is notoriously difficult with imaging alone 1
• Enlarged inguinal nodes are frequently reactive rather than malignant 1
• Pelvic nodal metastases may be smaller than 0.5 cm, making routine radiologic evaluation with CT and PET potentially unreliable 1

Impact on Treatment Planning:

• Confirmation of nodal involvement may influence radiation field planning
• There is potential additional morbidity from irradiation of the inguinal regions if not necessary 1
• Accurate nodal staging is important as nodal involvement is a significant prognostic factor 1

Pitfalls to Avoid

1. Do not assume all enlarged nodes are malignant

   • High prevalence of enlarged and reactive inguinal lymphadenopathy exists in these patients 1

2. Do not omit inguinal node assessment

   • Nodal involvement is an independent factor associated with locoregional failure and adverse overall survival 1

3. Do not rely solely on size criteria for determining malignancy

   • Metastatic nodes may be small (<0.5 cm) and still harbor disease 1

4. Do not delay treatment for extensive nodal workup in cases with obvious nodal disease

   • When nodes clearly show features of malignancy, proceeding directly to chemoradiation is appropriate

In summary, while FNA is not mandatory for all patients with anal cancer before starting chemoradiation, it plays an important role in confirming nodal status when imaging findings are equivocal and when the results would alter treatment planning. The decision should be guided by clinical examination findings and imaging results, with FNA reserved for cases where nodal status remains uncertain after standard imaging.