Management of Papillary Thyroid Microcarcinoma
Active Surveillance as First-Line Management
Active surveillance should be the first-line management approach for low-risk papillary thyroid microcarcinoma (PMC) rather than immediate surgery, as it is safer, less costly, and helps avoid adverse surgical events while maintaining excellent outcomes. 1
Definition and Classification of PMC
- PMC is defined as papillary thyroid carcinoma measuring 10 mm or smaller 1
- Not all PMCs are the same - they can be categorized into different risk groups 2:
- Low-risk PMC: asymptomatic, no clinical node metastasis, no distant metastasis, no extrathyroid extension
- High-risk PMC: presence of clinical node metastasis, distant metastasis, or invasion to surrounding structures
Evidence Supporting Active Surveillance
- Most low-risk PMCs remain indolent with very slow or no progression during active surveillance 1
- Long-term studies from Japanese hospitals show excellent outcomes 1:
- Tumor enlargement was detected in only 4.9% of patients at 5 years and 8.0% at 10 years
- Novel lymph node metastasis appeared in only 1.7% of patients at 5 years and 3.8% at 10 years
- No patients developed distant metastasis or died of thyroid carcinoma during active surveillance 1
- Even patients who underwent surgery after detection of progression signs showed no significant recurrence 1
Patient Selection for Active Surveillance
Suitable Candidates for Active Surveillance
- Asymptomatic PMCs without high-risk features 1
- PMCs ≤10 mm without clinical node metastasis or distant metastasis 1
- PMCs without clinical evidence of significant extrathyroid extension 1
Contraindications for Active Surveillance
- Clinically apparent lymph node metastasis 1
- Distant metastasis (very rare) 1
- Signs or symptoms of invasion to the recurrent laryngeal nerve or trachea 1
- High-grade malignancy on cytology (very rare) 1
- Tumors located near the recurrent laryngeal nerve or trachea (relative contraindication) 1
Active Surveillance Protocol
- Initial diagnosis via fine-needle aspiration cytology (FNAC) for suspicious nodules ≥5 mm 1
- Follow-up visits:
- Monitoring parameters:
Age Considerations
- Interestingly, PMCs in younger patients (<40 years) are more likely to progress than those in elderly patients 1
- This is in contrast to clinical papillary carcinoma, where older age is associated with worse prognosis 1
- Active surveillance can be considered for all adult age groups, with elderly patients having the lowest risk of progression 1
Surgical Management When Indicated
Surgery is indicated in specific circumstances:
- For high-risk PMCs with aggressive features 1
- When progression is detected during active surveillance 1:
- Significant tumor enlargement (typically >3 mm increase)
- Development of lymph node metastasis
- Development of local invasion
Surgical Approach When Needed
- For low-risk PMC that shows progression: thyroid lobectomy may be sufficient 3
- For high-risk PMC: total thyroidectomy with appropriate lymph node dissection 3
Implementation Considerations
- Active surveillance for PMC has been incorporated into guidelines in Japan (2010) and the United States (2015) 1
- Patient acceptance of active surveillance has increased over time as evidence of its safety has accumulated 1
- The rate of active surveillance in one Japanese hospital increased from 30% (1993-1997) to 88% (after 2014) 1
Pitfalls and Caveats
- Proper ultrasound technique and experience are essential for accurate monitoring 1
- Patients require thorough education about the indolent nature of most PMCs to reduce anxiety 4
- Continuous follow-up is necessary, as a small percentage of tumors may progress even after years of stability 1
- Some clinicians may still prefer immediate surgery due to personal practice patterns, despite growing evidence supporting active surveillance 1