Tall Cell Subtype of Papillary Thyroid Carcinoma: A Comprehensive Review

Epidemiology:
- The tall cell subtype of papillary thyroid carcinoma (PTC-TC):
  - Accounts for approximately 3% to 5% of all PTCs
    - Its incidence has been rising:
      - Partly due to evolving diagnostic criteria
- The WHO 5th edition (2022) defines PTC-TC as:
  - PTC with ≥ 30% tall cells:
    - Height-to-width ratio ≥ 3:1
- Patients tend to be older:
  - Mean ~ 50 years vs. 42 for classic PTC
- PTC-TC have higher rates of:
  - Extrathyroidal extension (~ 60%)
  - Vascular invasion (~ 15%)
  - Lymph node metastasis
  - Advanced stage at presentation
- Recurrence rates range from:
  - 27% to 42% compared to 16% to 31% for classic PTC
- 5-year disease-specific survival of:
  - Approximately 82% vs. 98% for all PTC
- An important recent distinction is:
  - Between PTC-TC (without high-grade features) and high-grade differentiated thyroid carcinoma with tall cell phenotype (HGDTC-TC):
    - Defined by ≥ 5 mitoses / 2 mm² and / or tumor necrosis
      - When HGDTC-TC is excluded PTC-TC has a more indolent course (10-year disease-specific survival ~99%)
Genetics and Molecular Features:
- BRAF V600E mutation:
  - Present in ~ 80% to 90% of cases:
    - Drives MAPK pathway activation and suppresses sodium-iodide symporter expression:
      - Contributing to RAI refractoriness
- TERT promoter mutations:
  - Independent predictor of recurrence:
    - More frequent in PTC-TC
- BRAF V600E + TERT co-mutation:
  - Identifies a subset with particularly poor outcomes
Surgical Management:
- Type of Thyroidectomy:
  - Standard indications for total thyroidectomy apply:
    - Distant metastases
    - Extrathyroidal extension
    - Lateral or gross central neck node metastases
    - Tumor > 4 cm
    - Bilateral disease
  - For tumors 1 cm to 4 cm without these features:
    - Either total thyroidectomy or lobectomy may be considered
- Key evidence:
  - A 2026 SEER analysis of 1,463 PTC-TC patients showed total thyroidectomy had superior cancer-specific survival vs. lobectomy:
    - 5-year CSS 97.8% vs. 90.7%, p = 0.019, independent of RAI
  - A Memorial Sloan Kettering study of T1 / T2 N0 PTC-TC:
    - Found no difference in outcomes with lobectomy alone, with 100% disease-specific survival in both groups
- Summary:
  - For small (T1 / T2), node-negative PTC-TC without high-grade features:
    - Lobectomy may be adequate
  - Larger or higher-stage tumors:
    - Should undergo total thyroidectomy
Central Compartment Neck Dissection:
- Therapeutic central neck dissection:
  - Recommended for clinically involved nodes (cN1a)
- Prophylactic central neck dissection:
  - Not routinely indicated per NCCN
- Thorough preoperative ultrasound of central and lateral compartments is essential:
  - With FNA of suspicious lateral nodes
Radioactive Iodine (RAI):
- NCCN classifies tall cell histology as a “high-risk subtype”:
  - For which RAI is selectively recommended based on the combination of clinical factors
- PTC-TC is classified in the ATA intermediate risk category
- Key considerations:
  - BRAF V600E-driven PTC-TC downregulates the sodium-iodide symporter:
    - Making these tumors frequently RAI-refractory
  - For tumors > 2 cm:
    - RAI after total thyroidectomy improved overall survival:
      - 83.4% vs. 70.0%
  - For tumors ≤ 2 cm:
    - No survival benefit from RAI was demonstrated
  - A SEER-based propensity-matched study:
    - Found no significant CSS benefit from RAI in PTC-TC overall:
      - HR 0.54, 95% CI 0.25–1.17
  - Repeated RAI should be limited to patients demonstrating continued therapeutic response
Follow-Up:
- After total thyroidectomy with RAI, recommended surveillance includes:
  - Physical examination, TSH, thyroglobulin (Tg), and anti-thyroglobulin antibodies (TgAb)
  - Neck ultrasound at 6 to 12 months, then every 1 to 3 years for 5 to 8 years, then discontinue
- Rising Tg or new TgAb:
  - Should prompt additional imaging:
    - Neck CT / MRI, chest / abdomen CT, FDG-PET, or RAI imaging
- TSH suppression with levothyroxine:
  - Per risk stratification
- For patients with no evidence of disease (NED) at low risk after 10 to 15 years:
  - No further thyroid cancer monitoring is indicated
RAI-Refractory Disease:
- For RAI-refractory progressive disease:
  - Molecular analysis for actionable alterations should be pursued:
    - BRAF V600E → dabrafenib / trametinib or vemurafenib / cobimetinib
    - RET fusions → selpercatinib or pralsetinib
    - NTRK fusions → larotrectinib or entrectinib
    - ALK fusions → targeted therapy
References:
- Shi X, Liu R, Basolo F, et al. Differential Clinicopathological Risk and Prognosis of Major Papillary Thyroid Cancer Variants. J Clin Endocrinol Metab. 2016.
- Wu SS, Joshi N, Sharrett J, et al. Risk Factors Associated With Recurrence and Death in Patients With Tall Cell Papillary Thyroid Cancer. JAMA Otolaryngol Head Neck Surg. 2023.
- Holoubek SA, MacKinney EC, Khokar AM, et al. Radioactive Iodine Does Not Improve Overall Survival for Patients With Aggressive Variants of Papillary Thyroid Carcinoma Less Than 2 Cm. Surgery. 2022.
- Jin X, Koga S, Zhou X, Khan NZ, Baloch ZW. Clinicopathologic Characteristics of Papillary Thyroid Carcinoma, Tall Cell Subtype and Subtype With Tall Cell Features, an Institutional Experience. Hum Pathol. 2025.
- Parvathareddy SK, Siraj AK, Qadri Z, et al. Tall Cell Variant Histology Predicts Poorer Disease-Free Survival in Papillary Thyroid Carcinoma: A Propensity-Matched Cohort Study. World J Surg. 2025.
- Ghossein R, Katabi N, Dogan S, et al. Papillary Thyroid Carcinoma Tall Cell Subtype (PTC-TC)