Preoperative calcitonin levels are predictive of tumor size and postoperative calcitonin normalization in medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) is a calcitonin (CT)-secreting endocrine tumor. Although plasma CT level is a specific and sensitive marker of MTC, its preoperative usefulness in predicting tumor size and postoperative CT n ormalization has not been documented. From a nationwide database set up by the French CT Tumor Study Group, 226 MTC patients were selected according t o the following criteria: preoperative CT level determination by an immunor adiometric assay (normal value, < 10 pg/mL) within the 6 months prior to su rgery, total thyroidectomy and diagnosis of MTC ascertained by histological report including tumor size. Patients were 129 females and 97 males (femal e/male ratio, 1.3). One hundred and twelve patients (49.6%) had the sporadi c variety of the disease, 74 (32.7%) had multiple endocrine neoplasia 2A, t hree (1.3%) had multiple endocrine neoplasia 2B, and 37 (16.4%) had familia l MTC. Median age at diagnosis was 44.8 yr (range, 4.9-80.1 yr). Complete n eck dissection was performed in 159 patients (70.4%). Postoperative CT norm alization was ascertained by negative response of CT to pentagastrin stimul ation (< 10 pg/mL) in 94 patients. Seventy-one patients were considered as not cured because of residual tumor tissue and/or elevated CT levels. Media n tumor size was 11.0 mm (range, 0.2-80.0 mm), significantly larger in fema les (15.0 vs. 8.0 mm, P < 0.05), and in sporadic forms (15.0 vs. 7.0 mm, P < 0.05). Tumor size was significantly correlated (r(2) = 0.52, P < 0.01) wi th preoperative CT levels, the relationship being more straight in familial (r2 = 0.71) than in sporadic (r(2) = 0.36) forms. Furthermore, preoperativ e CT levels under 50 pg/mL appeared to be predictive of postoperative CT no rmalization (44 of 45 patients). However, higher CT levels did not mean abs ence of postoperative CT normalization (50 of 120 patients). We conclude th at low preoperative CT levels are predictive of tumor size and postoperativ e CT normalization.