Serum Thyroglobulin Improves the Sensitivity of the McGill Thyroid Nodule Score for Well-Differentiated Thyroid Cancer.
Background: The McGill Thyroid Nodule Score (MTNS) is a scoring system elaborated to help physicians to assess the preoperative risk that a thyroid nodule is malignant. It uses 22 different known risk factors for thyroid cancer (radiation exposure, microcalcifications on ultrasound, positive HBME-1 stain on biopsy, etc) and attributes a percentage risk that the nodule is malignant. Recently, preoperative thyroglobulin (Tg) levels has been shown to correlate with the risk of malignancy. The aim of this study was to incorporate Tg levels into the already established MTNS. Methods: This is a retrospective analysis of 184 thyroidectomy patients at the McGill University Thyroid Cancer Centre. Patients with preoperative Tg levels were included in the study, and patients with incidental papillary microcarcinoma without extrathyroidal extent on final pathology were excluded. MTNS scores were calculated for all patients. Preoperative Tg levels of 75ng/mL added 1 point to the MTNS, and levels of 187.5ng/mL added 2 points. The new score is named MTNS+. Results: Malignancy rates were calculated for each MTNS+ score. Patients with a score of 0-1 were <5% at risk of malignancy, the malignancy rate for scores from 2-3 was 14.29%, followed by 28.95% for scores from 4-6, 32.65% for scores from 7-8, 64.86% from scores from 9-11, 71.43% for scores from 12-14, 78.57% for scores from 15-18, and 92.31% for scores from 19-22. All patients (5 of 5) with an MTNS+ score of 23 or more had a malignant final pathology result. Patients with scores >8 had a relative risk of 2.5 (95% CI 1.79-3.49) of malignancy compared to patients with lower scores. MTNS+ showed good specificity at higher scores, with 89%, 96%, and 100% at scores above 11, 14, and 20, respectively. Compared to MTNS, adding Tg levels did not improve positive predictive values (PPV) or specificity, but improved sensitivity by 7.89% at scores >8, and by up to 10.48% for scores >7. Conclusion: This study shows that adding Tg to the MTNS, increases the sensitivity of this scoring system. Moreover, it suggests that a combined scoring system such as the MTNS+ can accurately stratify the risk of well-differentiated malignancy in patients with thyroid nodules.