Advancements in the Treatment of Differentiated Thyroid Cancer (DTC)

Radioiodine Ablation

  • The American Thyroid Association (ATA) recommends radioiodine (RAI) adjuvant therapy for:
    • High risk DTC patients after total thyroidectomy
  • Prior to RAI therapy:
    • Serum TSH, thyroglobulin (Tg), and anti-Tg antibody measurements should be obtained
  • Patients should be instructed to:
    • Maintain a low iodine diet (50 mg / day) for 1 to 2 weeks
    • And undergo thyroid hormone withdrawal
  • Levothyroxine (LT4):
    • Should be discontinued 3 to 4 weeks prior to RAI, and
  • Liothyronine (LT3):
    • Should be discontinued 2 weeks prior to therapy
  • ATA low and intermediate risk DTC patients and patients with contraindications to a hypothyroid state:
    • May undergo recombinant human TSH stimulation instead of thyroid hormone withdrawal
  • The 5-year follow-up results of the ESTIMABL1 trial:
    • A randomized control trial investigating rhTSH versus thyroid hormone withdrawal and low activity (1.1 GBq) versus high activity (3.7GBq) RAI in patients with low-risk DTC:
      • Showed no evidence of disease regardless of preparation method or radioiodine dose used, providing further support for the use of rhTSH and 1.1 GBq radioactive iodine in these patients
  • For advanced DTC:
    • Dosimetry might be appropriate to quantify RAI uptake and determine dosing given the variability from person to person, and within cells of the same tissue
  • The goals of RAI therapy include:
    • Destroying occult disease foci
    • Eliminating residual healthy tissue that may serve as a locus for neoplastic transformation
    • Improving the specificity of Tg as a tumor marker, and of whole body RAI scans during long-term surveillance
  • A dose of 30mCi is recommended over higher doses in lower-risk patients, but high-risk patients may require 100 to 200 mCi
  • During RAI ablation, 131I is taken up by follicular thyroid cells, where the molecules accumulate and undergo beta decay:
    • This process is optimized by functional sodium iodide symporter expression (NIS):
      • Dedifferentiating tumors lose NIS expression and become fluorodeoxyglucose (FDG) avid as they lose RAI avidity:
      • For this reason, FDG-PET (positron emission tomography) positive tumors:
        • Tend to be more aggressive and unlikely to respond to RAI
  • Age greater than 40 years, large tumor burden, and Hürthle cell histology:
    • Are also indicators of poor response
  • MAPK and PI3K / AKT activation:
    • Is thought to decrease NIS activity
  • Tumors with RAS mutations may be more likely to be RAI avid than those with BRAF and TERTmutations
  • Side effects of RAI therapy include:
    • Nausea
    • Temporary or permanent salivary gland and lacrimal duct dysfunction
    • Sialadenitis
    • Parotitis
    • Thyroiditis
    • Bone marrow and gonadal dysfunction
      • Adequate hydration might help alleviate symptoms
    • There is also a risk of second primary cancer of:
      • Soft tissue, salivary gland, colon, and blood, associated with higher cumulative doses
  • Less than 10% of DTC patients will develop metastatic disease
    • Of these, approximately one in three experience complete remission after RAI therapy
  • The ATA recommends a whole body scan with or without single photon emission computed tomography (SPECT) / computed tomography (CT) to determine RAI avidity for residual structural disease after therapy

#Arrangoiz #ThyroidSurgeon #ThyroidCancer #ThyroidExpert #CancerSurgeon #HeadandNeckSurgeon #EndocrineSurgery #MountSinaiMedicalCenter #MSMC #Miami #Mexico #RAI #RadioActiveIodine

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