Diagnostic Follow-up

Importance of Follow-up and Approaches

Measurement of serum Tg levels is an important modality to monitor patients for residual or recurrent disease. Stimulated Tg testing may be performed with Thyrogen or thyroid hormone withdrawal.

Approximately 30% of patients with well-differentiated thyroid cancer experience recurrence, and one-third of the recurrences may not become evident until 10 or more years after initial treatment.1 Given that more than 50% of people diagnosed as having thyroid cancer are relatively young (20-54 years old)2, routine follow-up of these patients is important. According to the American Thyroid Association, accurate surveillance for possible recurrence in patients thought to be free of disease is a major goal of long-term follow-up. Tests used for determination of freedom from disease include3:

  • Clinical monitoring
  • Thyroglobulin (Tg) testing during thyroxine suppression or after TSH-stimulation
  • Neck Ultrasonography
  • Radioiodine imaging with whole-body scans

The 2015 American Thyroid Association guidelines specify that in low-risk and intermediate-risk patients who have had remnant ablation or adjuvant therapy and negative cervical ultrasound findings, serum Tg should be measured approximately every 6 months during the initial 6 to 18 month follow-up period in those on thyroxine therapy, using a sensitive Tg assay (<0.2 ng/mL), or after TSH stimulation, to verify absence of disease (excellent response). The highest degrees of sensitivity for serum Tg are noted following thyroid hormone withdrawal or stimulation using rhTSH.

Repeat TSH-stimulated Tg testing is not recommended for low and intermediate risk patients who have an excellent response to therapy. Subsequent TSH-stimulated testing may be considered for patients with an indeterminate, biochemical incomplete, or structural incomplete response following either additional therapies or a spontaneous decline in Tg values on thyroid hormone therapy over time to reassess response to therapy.3

Use of Thyrogen in Follow-up of Patients with Well-Differentiated Thyroid Cancer4

Study Design

  • In a prospective, randomized, phase 3 clinical trial with a cross-over, nonblinded design, patients with well-differentiated thyroid cancer were evaluated to compare Tg levels obtained after Thyrogen, to those at baseline and to those after thyroid hormone withdrawal.
  • Patients who were included in the Tg analysis were those who had undergone total or near-total thyroidectomy with or without 131I ablation, had < 1% uptake in the thyroid bed on a scan after thyroid hormone withdrawal, and did not have detectable anti-Tg antibodies.
  • The maximum Thyrogen Tg value was obtained 72 hours after the final Thyrogen injection, and this value was used in the analysis.

Stimulated Thyroglobulin (Tg) vs nonstimulated Tg testing4

Among patients with metastatic disease confirmed by a post-treatment scan or by lymph node biopsy (35 patients), Thyrogen Tg was positive (≥2.5 ng/mL) in all 35 patients, while Tg on thyroid hormone suppressive therapy was positive (≥2.5 ng/mL) in 79% of these patients.

As with thyroid hormone withdrawal, the intrapatient reproducibility of Thyrogen testing with regard to both Tg stimulation and radioiodine imaging has not been studied.

References

  1. Mazzaferri EL. An overview of the management of papillary and follicular thyroid carcinoma. Thyroid. 1999;9:421-427.
  2. SEER. Thyroid cancer. 2015. http://seer.cancer.gov/statfacts/html/thyro.html. Accessed Nov 1, 2015.
  3. Haugen BR, Alexander EK, Bible KC, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid. 2015; doi: 10.1089/thy.2015.0020.
  4. Thyrogen (thyrotropin alfa for injection) Package Insert. Cambridge, MA. Genzyme Corp. 2014.

INDICATIONS AND USAGE
Thyrogen is a thyroid stimulating hormone indicated for:

Diagnostic: Use as an adjunctive diagnostic tool for serum thyroglobulin (Tg) testing with or without radioiodine imaging in the follow-up of patients with well-differentiated thyroid cancer who have previously undergone thyroidectomy.

Limitations of Use:
Thyrogen-stimulated Tg levels are generally lower than, and do not correlate with Tg levels after thyroid hormone withdrawal. Even when Thyrogen-Tg testing is performed in combination with radioiodine imaging, there remains a risk of missing a diagnosis of thyroid cancer or underestimating the extent of the disease. Anti-Tg Antibodies may confound the Tg assay and render Tg levels uninterpretable.

Ablation
: Use as an adjunctive treatment for radioiodine ablation of thyroid tissue remnants in patients who have undergone a near-total or total thyroidectomy for well-differentiated thyroid cancer and who do not have evidence of distant metastatic thyroid cancer.

Limitations of Use:
The effect of Thyrogen on long term thyroid cancer outcomes has not been determined.

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Thyrogen® (thyrotropin alfa for injection) 0.9 mg/mL after reconstitution

IMPORTANT SAFETY INFORMATION

WARNINGS AND PRECAUTIONS

There have been reports of death in non-thyroidectomized patients and in patients with distant metastatic thyroid cancer in which events leading to death occurred within 24 hours after administration of Thyrogen.

Caution should be exercised in patients who have substantial thyroid tissue still in situ or functional thyroid cancer metastases, specifically in the elderly and those with a known history of heart disease.

Hospitalization for administration of Thyrogen and post-administration observation in patients at risk should be considered.

There are post marketing reports of stroke in young women with risk factors for stroke, and neurological findings suggestive of stroke (e.g., unilateral weakness) occurring within 72 hours of Thyrogen administration in patients without known central nervous system metastases.

Patients should be well-hydrated prior to treatment with Thyrogen.

Sudden, rapid and painful enlargement of residual thyroid tissue or distant metastases can occur following treatment with Thyrogen.

Pretreatment with glucocorticoids should be considered for patients in whom tumor expansion may compromise vital anatomic structures.

ADVERSE REACTIONS

The most common adverse reactions reported in clinical trials were nausea and headache.

USE IN SPECIFIC POPULATIONS

Pregnancy Category C: Animal reproduction studies have not been conducted with Thyrogen. It is also not known whether Thyrogen can cause fetal harm when administered to a pregnant woman or can affect reproductive capacity. Thyrogen should be given to a pregnant woman only if clearly needed.

Nursing Mothers: It is not known whether the drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Thyrogen is administered to a nursing woman.

Pediatric Use: Safety and effectiveness in pediatric patients have not been established.

Geriatric Use: Results from controlled trials do not indicate a difference in the safety and efficacy of Thyrogen between adult patients less than 65 years and those over 65 years of age.

Renal Impairment: Elimination of Thyrogen is significantly slower in dialysis-dependent end stage renal disease patients, resulting in prolonged elevation of TSH levels.

INDICATIONS AND USAGE

Thyrogen is a thyroid stimulating hormone indicated for:

Diagnostic: Use as an adjunctive diagnostic tool for serum thyroglobulin (Tg) testing with or without radioiodine imaging in the follow-up of patients with well-differentiated thyroid cancer who have previously undergone thyroidectomy.

Limitations of Use:

  • Thyrogen -stimulated Tg levels are generally lower than, and do not correlate with Tg levels after thyroid hormone withdrawal.
  • Even when Thyrogen -Tg testing is performed in combination with radioiodine imaging, there remains a risk of missing a diagnosis of thyroid cancer or underestimating the extent of the disease.
  • Anti-Tg Antibodies may confound the Tg assay and render Tg levels uninterpretable.

Ablation: Use as an adjunctive treatment for radioiodine ablation of thyroid tissue remnants in patients who have undergone a near-total or total thyroidectomy for well-differentiated thyroid cancer and who do not have evidence of distant metastatic thyroid cancer.

Limitations of Use:

  • The effect of Thyrogen on long term thyroid cancer outcomes has not been determined.

See full Prescribing Information for more details.