The Medullary Thyroid Cancer Marker
Calcitonin is a hormone produced by thyroid C-cells that lowers blood calcium. Clinically, its main importance isn't calcium regulation—it's as a tumor marker for medullary thyroid cancer (MTC). C-cells are the ones that become cancerous in MTC, and they produce large amounts of calcitonin. Elevated calcitonin with a thyroid nodule is a red flag.
What is Calcitonin?
Calcitonin is a 32-amino acid peptide from thyroid parafollicular C-cells. Inhibits osteoclasts (reduces bone resorption) and promotes renal calcium excretion. Clinically used as MTC tumor marker. Pentagastrin or calcium stimulation tests improve sensitivity for early MTC detection.
↑ What High Calcitonin Means
Medullary thyroid cancer is the primary concern. Also mildly elevated in: C-cell hyperplasia (pre-malignant), chronic kidney disease, other neuroendocrine tumors, proton pump inhibitors, and pregnancy. Calcitonin >100 pg/mL: high suspicion for MTC.
Common symptoms:
Thyroid nodule (often incidental) · If MTC: neck mass, hoarseness, dysphagia · If MEN2B: marfanoid habitus, mucosal neuromas · Diarrhea (secretory—from calcitonin excess in advanced MTC)
↓ What Low Calcitonin Means
Not clinically significant (thyroidectomy patients will have undetectable calcitonin).
Common symptoms:
No symptoms
Why It Matters
When normal:
Primary tumor marker for medullary thyroid cancer
Screens MEN2 family members for MTC
Monitors MTC recurrence after surgery
Part of thyroid nodule workup when MTC suspected
Risks if abnormal:
Elevated: must rule out medullary thyroid cancer
>100 pg/mL: very high MTC probability
MTC in MEN2A/2B: screen family members (RET gene mutation)
What Can Cause Abnormal Levels?
Medullary Thyroid Cancer
60% likelyMTC produces calcitonin. Level correlates with tumor burden. Doubling time predicts prognosis.
C-Cell Hyperplasia
20% likelyPre-malignant proliferation of C-cells. May precede MTC in MEN2 families.
Chronic Kidney Disease
Reduced clearance causes mild calcitonin elevation.
Other Neuroendocrine Tumors
Pheochromocytoma, carcinoid can produce calcitonin.
Proton Pump Inhibitors
PPIs can mildly elevate calcitonin.
What You Can Do
If calcitonin >100 with thyroid nodule: strong suspicion for MTC
Impact: Refer to endocrine surgery \u00B7 Timeline: Urgent
If MTC confirmed: screen for RET gene mutation (MEN2)
Impact: MEN2 requires screening for pheochromocytoma and hyperparathyroidism \u00B7 Timeline: At diagnosis
If lifestyle changes aren't enough:
Family members of MEN2 patients: genetic testing for RET mutations
Impact: Prophylactic thyroidectomy prevents MTC in carriers \u00B7 Timeline: One-time
Recommended retest: Post-thyroidectomy: q3-6 months for MTC surveillance
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