ROUTINE MEASUREMENT OF SERUM CALCITONIN IN NODULAR THYROID-DISEASES ALLOWS THE PREOPERATIVE DIAGNOSIS OF UNSUSPECTED SPORADIC MEDULLARY-THYROID CARCINOMA

To assess whether routine measurement of serum calcitonin (CT) could i mprove the preoperative diagnosis of sporadic medullary thyroid carcin oma (MTC), 1385 consecutive patients presenting for nodular thyroid di sease during the year 1991 were submitted to serum CT determination an d fine needle aspiration cytology (FNAC). The clinical diagnosis was n ontoxic nodular goiter in 1197 (86.4%) patients, toxic multinodular go iter in 65 (4.7%), autonomously functioning thyroid nodule (AFTN) in 6 4 (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 stud ied. Patients with FNAC suspicious of any kind of thyroid carcinoma an d patients with elevated basal and pentagastrin-stimulated serum CT, r egardless of the results of FNAC, were submitted to surgery. Eight (0. 57%) patients (7 with nontoxic nodular goiter and 1 with AFTN) had ele vated basal serum CT levels, ranging between 55-10,000 pg/mL. The pent agastrin 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 tot al 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 undetectabl e 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 respon se to pentagastrin. Forty-four patients in the group with normal serum CT levels had FNAC suspicious for differentiated thyroid carcinoma an d were treated by surgery. Differentiated thyroid carcinoma, mostly pa pillary, was confirmed at histology in 43 subjects (3.1% of all thyroi d nodules). In conclusion, the results of our study indicate that seru m CT measurement is useful for the screening of sporadic MTC in patien ts with thyroid nodule(s). The prevalence of MTC, diagnosed by serum C T 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 mea surement was superior to FNAC in suggesting the diagnosis of MTC and w as devoid of falsely positive results. Increasing the diagnostic accur acy helped the surgeon to perform more radical treatment of MTC, thus achieving frequent normalization of postoperative serum CT levels. Whe ther this result indicates definitive cure remains to be established o n the basis of longer follow-up. We recommend serum CT measurement in the diagnostic evaluation of thyroid nodules.