Does a patient with multifocal thyroid papillary carcinoma (thyroid cancer) with two foci, one measuring 1.1 cm in the right lobe and another measuring 0.6 cm in the left lobe, without angioinvasion (invasion of blood vessels) or lymph node (LN) metastasis, require radioiodine (I-131) therapy?

Radioiodine Therapy for Multifocal Papillary Thyroid Carcinoma

Radioiodine therapy is not necessary for this patient with multifocal papillary thyroid carcinoma with small tumor foci (1.1 cm and 0.6 cm), clean borders, no angioinvasion, and no lymph node metastases.

Risk Stratification and Decision Algorithm

This patient falls into the low-risk category based on the following features:

• Multifocal papillary thyroid carcinoma with primary tumor size 1.1 cm
• Secondary focus of 0.6 cm
• No extrathyroidal extension (clean borders)
• No angioinvasion
• No lymph node metastasis

According to the ESMO clinical practice guidelines 1, this patient would be classified as low risk with an estimated recurrence risk of only 1-6%. The risk stratification system clearly identifies patients with the following characteristics as low risk:

• No macroscopic tumor remnants after resection
• No locoregional invasion
• No lymph node metastases
• No vascular invasion
• Non-aggressive histology

Radioiodine Therapy Recommendations

The decision for radioiodine therapy should be based on risk stratification:

1. For very low-risk patients (unifocal tumors <1 cm with favorable histology):

   • Radioiodine ablation is not indicated 1

2. For low-risk patients (like our case with multifocal disease but otherwise favorable features):

   • The evidence is mixed, but recent guidelines suggest radioiodine may be omitted
   • The ESMO guidelines from 2010 1 previously recommended radioiodine for all except very low-risk patients
   • However, more recent evidence suggests minimal benefit for low-risk patients without other adverse features

3. For intermediate and high-risk patients:

   • Radioiodine ablation is clearly recommended 1

Specific Considerations for Multifocality

Multifocality has been traditionally considered a risk factor, but recent evidence shows:

• For multifocal papillary microcarcinomas (<1 cm), multifocality does not significantly impact prognosis 2
• For multifocal macroscopic PTC without bulky nodal involvement (as in this case), the risk of recurrence is low 3
• The prognostic significance of multifocality appears to be more relevant for tumors >1 cm 2, but other adverse features must also be present

Important Caveats and Considerations

• Total thyroidectomy is the appropriate surgical approach for multifocal disease, which this patient has presumably already undergone
• Close monitoring with thyroglobulin measurements and neck ultrasound is essential regardless of the decision about radioiodine
• If other adverse features were present (aggressive histology, extrathyroidal extension, lymph node metastasis), the recommendation would change in favor of radioiodine therapy
• The presence of BRAF V600E mutation (if tested) might influence this decision, as it can be associated with more aggressive behavior 1

Follow-up Recommendations

Even without radioiodine therapy, this patient should receive:

• TSH suppression therapy with levothyroxine
• Regular monitoring with thyroglobulin measurements
• Periodic neck ultrasound examinations
• More intensive surveillance if any high-risk features are subsequently identified

In conclusion, based on the most recent evidence and guidelines, this patient with small multifocal papillary thyroid carcinoma without other adverse risk factors does not require radioiodine therapy, as it would provide minimal benefit while exposing the patient to unnecessary radiation.