Thyroid Cancer

Epidemiology

  • 16K cases per year, incidence increasing over last 25 years
  • Ave weight 20g

Pathology

Papillary

  • 80% of thyroid cancers
  • Recurrence rates: 9% nodal, 6% local, 5% metastatic after 25 years of follow up.
  • Solitary or multicentric nodules
  • low rate of metastases
  • associated with FAP (Gardner’s syndrome)
  • Psammoma bodies

Follicular

  • 10% of thyroid cancers
  • slightly worse overall survival of 92% compared to papillary
  • Nodal metastases are rare with nodal relapse 1% at 10 years
  • often invades capsule, vessels
  • 4-7% have distant metastasis ( bone, lung, liver ect.) at the time of diagnosis

Hurthle (Oncocytic)

  • follicular variant with 75% of cell in the follicular tumor exhibiting Hurthle cell or oncocytic features
  • 8-10% distant metastasis (slightly higher rate compared to Follicular).

Medullary

  • 5%, MEN I, IIA, IIB (often familial)
  • don’t take up Iodine
  • RET proto-oncogene.

Anaplastic

  • almost uniformly fatal from local progression.
  • Lymphoma
  • < 1% of all lymphomas
  • Almost all NHL (intermediate to high-grade) although MALT may also be present
  • Treatment Options (controversial)
  • EBRT + Doxorubicine-based chemotherapy
  • Surgical excision + Post-operative RT especially for 20-30% of patients with no extrathyroidal extension.
  • OS-5 70%

Thyroid Nodules

  • 20-30% of US population has palpable nodule, 50% by ultrasound, 80-90% by path after total thyroidectomy.
  • Worrisome nodules include: prior radiation, hard/fixed nodule, fixed VC, palpable neck nodes.
  • Scans: “cold nodules” – 20% malignant. “Hot nodules” – <5% malignant.
  • U/S: solid – 20% malignant. Cystic — <5% malignant.
  • Prognostics: Older (>45 y), male, T-stage all are bad. N-stage makes little difference.
  • “High Risk” -

Stage

T1 1cm N1a ipsilateral node(s) I Age<45 y, M0 Age45, T1N0
T2 >1 - 4cm N1b bilateral, contralateral, II Age<45, M1 Age45, T2-3 N0
T3 >4cm or mediastinal node(s) III Age 45 and T4N0 or N1
T4 Beyond capsule IV Age45 and M1

Treatment

I-131

  • The whole-body effective biological half-life of iodine-131 is 7.6 days
  • I-131 decays with a half-life of 8.0197 days with beta and gamma emissions.
  • Many experts do not recommend the use of radioiodine therapy for Hürthle, tall, insular, or medullary carcinoma as they concentrate radioiodine poorly or not at all

Papillary, Follicular and Hurthle Cell

Role of Post-operative (RRA)
Indications

  • Stage III /IV / II and ≥ 45-years-old
  • Most stage II and ≥ 45-years-old
  • Stage I with multifocal disease, nodal metastases, extrathyroidal or vascular invasion and/or more aggressive histologies.

Steps

  • Total Thyroidectomy – risk of recurrent laryngeal n., superior laryngeal n., hypoparathyroidism.
  • “High risk” patients should get T4 (levothyroxine) to suppress pituitary production of TSH to <0.5 mU/ml..
  • Stop T4 ~4 weeks prior to I-131 to rev-up I-uptake.
  • Can give T3 (cytomel) until 2 weeks prior (it has shorter half-life).
  • TSH should be 30 before giving I-131.
  • Scan 1 week prior I-131 for mets.
  • I-131 Ablation – standard dose 100mCi.

Dose

  • “low-risk” use 30-100 mCi
  • Microscopic residual or aggressive histology (tall cell, insular, columnar cell) 100-200 mCi

Definitive RAI (Radioacitive iodine)

  • Compared to RRA, larger doses of I-131 are given to destroy persistent neck disease or distant metastatic lesions. 50-125 mCi
  • Studies suggested that it be used routinely in high-risk patients with incompletely resected disease or distant metastatses.

External beam radiation
Indications

  • ≥ 45-years-old locally advanced disease with grossly visible extrathyroidal disease at the time of surgery
  • Patients with gross disease AND further surgery or I-131 is likely to be ineffective.

Doses for Papillary/Follicular/Medullary

  • CTV 45-50 Gy
  • Microscopic 55-60 Gy
  • Gross ≥ 65 Gy

Chemotherapy

  • No role as mono therapy
  • Doxorubicin could be considered as radiosensitizer for locally advanced tumors undergoing external beam radiotherapy

Medullary Carcinoma

  • Consider adjuvant RT in patients with
  • T4 disease with ≥ 1 cm disease or bilateral disease
  • See External beam radiation above

Anaplastic Thyroid Carcinoma

  • Total thyroidectomy if possible
  • Concurrent chemoradiation (hyperfractionation)
  • 1.5 BID to 60 Gy
Bibliography
1. Cooper DS, Doherty GM, Haugen BR, Kloos RT, Lee SL, Mandel SJ, Mazzaferri EL, McIver B, Sherman SI, Tuttle RM; The American Thyroid Association Guidelines Taskforce. Management guidelines for patients with thyroid nodules and differentiated thyroid cancer. Thyroid. 2006 Feb;16(2):109-42. No abstract available. PMID: 16420177
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