Surveillance

There are three different ways to detect if the cancer has recurred / persisted.

• Physical exam.
  • Feeling for a mass or enlarged lymph node in the neck.
• Ultrasound of the Neck – more sensitive than physical exam to pick up earlier / smaller growths of cancer.
  • Should assess the remaining thyroid lobe for any pre-existing or new thyroid nodules that may meet criteria for FNA (if only a hemithyroidectomy was performed).
  • Inspect the lymph nodes in the central and lateral neck compartments for atypical features (e.g. enlarged, circular shape, loss of hilum, calcifications, cystic spaces, etc.).
  • Typically performed yearly.
    • Less frequently for low-risk cancers, more frequently for high-risk cancers or if recurrence is suspected.
  • If cancer persistence is suspected based on elevated thyroglobulin levels, but not detected on ultrasound of the neck you can consider looking with:
    • Iodine Whole Body Scan (WBS).
      • An I-123 tablet is swallowed and a scan of the entire body is performed to determine where the iodine is absorbed.
      • A focus of iodine absorption would indicate either residual normal thyroid tissue or possibly recurrent / persistent thyroid cancer cells.
      • The quality of these scans may be institution dependent and also requires that any residual thyroid cancer cells still absorb the iodine (aka iodine avid).
    • CT of the Neck and/or Chest with contrast.
      • CT can sometimes detect lymph nodes in areas where ultrasounds cannot (behind the esophagus or pharynx, in the upper chest / mediastinum, behind the carotid artery / internal jugular vein).
    • PET-CT scans can also be considered if the cancer is no longer iodine avid, with aggressive subtypes of WDTC (e.g. tall cell variant PTC or FTC / OCA with extensive angioinvasion), or not seen on CT of the Neck / Chest.
• Thyroglobulin (Tg) levels.
  • Tg is a protein made only by thyroid cells in the body and can easily be measured in the blood.
  • 6 weeks after total thyroidectomy, Tg levels can give an accurate measurement of how much thyroid tissue remains in the body, both normal and cancer cells.
    • It takes 6 weeks for Tg made previously by the thyroid to filter out of the blood.
  • If there are no thyroid cells (both normal and cancerous) in the body following surgery, the Tg level will be very low (< 1.0) or even undetectable (< 0.10).
    • Following hemithyroidectomy, Tg levels should be < 30.
  • If cancer cells remain in the body following treatment, Tg levels will be elevated (> 1.0).
    • Following hemithyroidectomy, Tg levels will often > 30.
  • If there is an Intermediate or High risk for cancer recurrence, Radioactive Iodine (RAI) can be considered to kill off any residual normal thyroid tissue (aka remnant ablation).
    • No matter how thorough a total thyroidectomy is performed, there are always some normal thyroid cells that will remain.
      • Typically, these cells are located where the thyroid attaches to the trachea near the recurrent laryngeal entry point into the larynx (Berry’s Ligament), from ectopic islands of thyroid tissue, or an incompletely removed pyramidal lobe.
      • These cells can produce enough thyroglobulin to be measured in the blood (typically < 1.0).
    • Remnant ablation makes any measured Tg levels much more sensitive and specific for detecting cancer and not normal thyroid cells.
  • Tg levels will remain elevated if only a hemithyroidectomy is performed.
    • Therefore, small changes in Tg levels will be much harder to detect, and it is not as sensitive of a detector for cancer recurrence.
    • This is something to consider when deciding between hemithyroidectomy and total thyroidectomy as surgical options.
  • Tg levels are also influenced by TSH levels in the blood.
    • If TSH levels are elevated, any remaining thyroid tissue will make more Tg and it will be elevated in the blood.
    • Therefore, TSH levels must also be measured at the same time as Tg to ensure that TSH is appropriately suppressed.
    • If the TSH level was not appropriately suppressed, the dose of thyroid hormone medication should be adjusted and the Tg levels should be measured again 4 weeks later.
  • Tg levels can be falsely low when there are antibodies (Ab) to the protein also present in the blood.
    • The combination of a Tg Ab attached to the Tg protein cannot be accurately measured.
    • Therefore, Tg Ab levels must always be measured with Tg levels to ensure that the measurement is accurate and reliable.
      • If Tg Ab levels are elevated, the Tg value measured may not be accurate.
      • If Tg Ab levels are elevated, they can be used as a surrogate tumor marker level to follow over time.
    • Tg LC/MS/MS is a new test developed to help accurately measure Tg levels when Ab’s are present.
      • Tg LC/MS/MS are not always accurate / trustworthy and therefore should always be followed closely with Tg Ab levels and ultrasound.
  • If Tg levels rise following surgery, it may be an indication that thyroid cancer cells are present or growing in the body.
    • Imaging studies should be performed to assess where this cancer tissue is.
      • Initially ultrasound of the neck, consider CT of the Neck with contrast or Iodine WBS if not seen on ultrasound.
        • In rare cases consider PET/CT.
    • If no obvious cancer cells are seen on imaging, surveillance should be performed more frequently.

This is an ongoing assessment that predicts risk for cancer recurrence based on information gathered during the 5-year surveillance period.

• Using imaging (ultrasound, CT Scan, and/or Iodine WBS) findings and tumor marker levels (thyroglobulin protein and thyroglobulin antibodies) measured in the blood over time.
• This dynamic risk assessment differs from the American Thyroid Association Risk Stratification System which is used to predict risk for cancer recurrence initially after surgery using only information from the pathology report.
• Excellent Response (risk for cancer present 5 years following treatment 1-4%)
  • Following Total Thyroidectomy:
    • Thyroglobulin (Tg) < 0.2.
    • Undetectable Tg Antibodies.
    • Negative Imaging.
  • Following Lobectomy:
    • Tg < 30 and stable.
    • Undetectable Tg Antibodies.
    • Negative Imaging.
• Indeterminate Response (risk for cancer present 5 years following treatment 15-20%).
  • Following Total Thyroidectomy:
    • Thyroglobulin (Tg) 0.2 – 1.0.
    • Stable or declining Tg Antibodies.
    • Non-specific findings on imaging.
  • Following Lobectomy:
    • Stable or declining Tg Antibodies.
    • Non-specific findings on imaging.
• Biochemical Incomplete Response (risk for cancer present 5 years following treatment 20%).
  • Following Total Thyroidectomy:
    • Tg > 1.0.
    • Increasing Tg Antibodies.
    • Negative imaging.
  • Following Lobectomy:
    • Tg > 30.
    • Increasing Tg Antibodies.
    • Negative Imaging.
• Structural Incomplete Response (risk for cancer present 5 years following treatment 50-85%).
  • Structural or functional evidence of cancer.

Dependent on initial risk for recurrence following surgery and dynamic risk assessment during surveillance.

• Initial measurement of labs (thyroglobulin and thyroglobulin antibodies levels, TSH) 6 weeks after surgery.
• If low risk for recurrence at 6 weeks based on pathology report and Tg levels, then repeat Tg labs and perform ultrasound at 6 months.
  • If continued low risk at 6 months, repeat Tg labs and ultrasound every 12 months until 5 years of surveillance concludes.
• If Intermediate to High risk for recurrence at 6 weeks, repeat Tg labs and perform ultrasound at 3 months.
  • If stable findings, repeat Tg labs and ultrasound every 6-12 months until 5 years of surveillance concludes.
• If the dynamic risk assessment changes during surveillance (e.g. rising Tg levels or new lesion noted on imaging), Tg labs and ultrasound should be performed more frequently.
• If there is high suspicion for persistent disease based on elevated Tg levels and no obvious sites of recurrence are seen on ultrasound, consider role for CT Neck with contrast, Whole Body Iodine Scan with I-123 (WBS), or PET-CT if the cancer is thought to no longer be iodine avid.
• If there is indeterminate to high suspicion for recurrent disease at the end of 5 years following treatment, surveillance should be continued indefinitely.