Objective: Sporadic medullary cancer of the thyroid is often diagnosed late beyond the surgically curable stage. The aim of this work was to assess the capacity of routine calcitonin assay as an early diagnosis test for medullary cancer in patients with a thyroid lesion.
Methods: Calcitonin was assayed (normal < 10 pg/ml) as a routine test from 1993-1995 in a series of 2975 patients seen for thyroid exploration. When baseline level was above 10 pg/ml, a pentagastrine test was performed (normal < 30 pg/ml). All patients with a calcitonin peak > or = 100 pg/ml after pentagastrin underwent surgery for suspected medullary cancer. Surgery for suspected malignancy, hyperthyroidism or locoregional functional disorders was also performed in 1494 of the included patients, independent of calcitonin level. Patients with personal or familial history of multiple endocrine disease were excluded. Fine needle aspiration was done in all patients with an unique or predominant thyroid nodule.
Results: Medullary cancer of the thyroid was demonstrated in 14 patients (0.47%). Among 8 patients with clinically patent tumor, the diagnosis was established in 3 on the basis of cytology results and elevated calcitonin level; in the 5 other cases, initial cytology was incorrect (anaplastic, papillary, thyroiditis) but correct diagnosis was established on the basis of high calcitonin levels. Diagnosis was suspected preoperatively in the 6 others solely because of high calcitonin; these patients had microlesions measuring 1.2-9 mm. None of the 7 patients with a medullary cancer measuring < 10 mm had node extension at surgery and all 7 attained biological cure. Among the 7 other patients with a lesion > 10 mm, calcitonin level returned to normal level in 3 and remained high in 2; the 2 others died with distant metastasis.
Conclusion: Routine assay of calcitonin in all patients with a thyroid nodule can improve preoperative diagnosis of medullary cancer of the thyroid and allows early diagnosis of latent infraclinical tumors.