To assess whether routine measurement of serum
calcitonin (CT) could improve the preoperative diagnosis of sporadic medullary
thyroid carcinoma (MTC), 1385 consecutive patients presenting for nodular
thyroid disease during the year 1991 were submitted to serum CT determination and fine needle aspiration cytology (FNAC). The clinical diagnosis was nontoxic
nodular goiter in 1197 (86.4%) patients, toxic multinodular
goiter in 65 (4.7%), autonomously functioning
thyroid nodule (AFTN) in 64 (4.6%), and autoimmune
thyroid disease (
Graves' disease or Hashimoto's
thyroiditis) with nodule(s) in 59 (4.3%). As controls, 177 patients with nonnodular
thyroid disease and 32 normal subjects were also studied. Patients with FNAC suspicious of any kind of
thyroid carcinoma and patients with elevated basal and
pentagastrin-stimulated serum CT, regardless of the results of FNAC, were submitted to surgery. Eight (0.57%) patients (7 with nontoxic
nodular goiter and 1 with AFTN) had elevated basal serum CT levels, ranging between 55-10,000 pg/mL. The
pentagastrin test was abnormal in all of them. FNAC was suggestive of MTC in 2,
thyroid carcinoma in 1, benign nodule in 3, and inadequate in 2. By histology, immunohistochemistry, and Northern blot analysis of total
tumor RNAs, MTC was confirmed in all patients, including the 1 with AFTN, who had the association of microfollicular
adenoma and a small MTC in the same lobe. After surgery, serum CT decreased to undetectable levels in 7 patients and remained undetectable in 6 of them during a mean follow-up of 22 months, although 1 of them had a positive response to
pentagastrin. Forty-four patients in the group with normal serum CT levels had FNAC suspicious for differentiated
thyroid carcinoma and were treated by surgery. Differentiated
thyroid carcinoma, mostly papillary, was confirmed at histology in 43 subjects (3.1% of all
thyroid nodules). In conclusion, the results of our study indicate that serum CT measurement is useful for the screening of sporadic MTC in patients with
thyroid nodule(s). The prevalence of MTC, diagnosed by serum CT measurement in a 12-month period, among an unselected series of 1385 patients with nodular
thyroid disease was surprisingly high: 0.57% of all
thyroid nodules and 15.7% of all
thyroid carcinomas. Serum CT measurement was superior to FNAC in suggesting the diagnosis of MTC and was devoid of falsely positive results. Increasing the diagnostic accuracy helped the surgeon to perform more radical treatment of MTC, thus achieving frequent normalization of postoperative serum CT levels. Whether this result indicates definitive cure remains to be established on the basis of longer follow-up.(ABSTRACT TRUNCATED AT 400 WORDS)