Thyroid Cancer Diagnosis and Management

Introduction to Thyroid Function Tests

Thyroid function tests (TSH, free T4, free T3) assess the thyroid gland's ability to produce and regulate thyroid hormones, not the presence of malignancy, as stated by the American Society of Clinical Oncology 1, 2, 3

Thyroid function tests are used post-treatment to monitor levothyroxine suppressive therapy adequacy, not to diagnose or detect cancer, according to the American Thyroid Association 1, 2, 3

Physical examination detecting thyroid nodules, neck ultrasound showing suspicious features, and fine-needle aspiration biopsy provide the diagnosis, as recommended by the National Comprehensive Cancer Network 1, 2, 3
Serum thyroglobulin (Tg) serves as the tumor marker for monitoring recurrence after total thyroidectomy, not TSH or thyroid hormones, as stated by the American Association of Clinical Endocrinologists 1, 2, 3

Two to three months after total thyroidectomy and radioiodine ablation, thyroid function tests (FT3, FT4, TSH) are obtained solely to verify adequate levothyroxine suppressive therapy dosing, according to the American College of Endocrinology 1, 2, 3, 4
The goal of TSH suppression varies by risk: <0.1 mIU/L for high-risk or persistent disease, 0.1-0.5 mIU/L for intermediate-risk, and 0.5-2 mIU/L for low-risk patients, as recommended by the European Thyroid Association 5

Ordering thyroid function tests to screen for or diagnose thyroid cancer wastes resources and provides no diagnostic value, as these tests measure hormone production capacity, not malignancy, according to the American Academy of Clinical Endocrinologists 6, 5
Assuming normal TSH excludes thyroid pathology is incorrect; thyroid cancer can coexist with completely normal thyroid function, requiring structural imaging (ultrasound) for detection, as stated by the Society of Nuclear Medicine and Molecular Imaging 1, 2

Patients on immune checkpoint inhibitors for metastatic cancer can develop hypophysitis causing central hypothyroidism, presenting with low free T4 and inappropriately low or normal TSH, as reported by the Journal for ImmunoTherapy of Cancer 7, 8, 9
Both TSH and free T4 should be ordered simultaneously in patients receiving immunotherapy, as TSH alone misses central hypothyroidism, according to the European Society for Medical Oncology 6, 5