Endocrine Abstracts

Introduction: Despite its neuroendocrine origin, only recently an international study group proposed a dedicated grading system (IMTCGS) for medullary thyroid carcinoma (MTC). IMTCGS is an independent and powerful tool able to predict disease specific survival (DSS) as well as distant metastasis-free (DMFS) and locoregional recurrence-free survivals (LRFS), regardless of other risk factors, including staging.

Objectives: To evaluate the performance of IMTCGS in predicting DSS, DMFS and LRFS in a series of sporadic MTC divided according to different clinical presentations (stage I-II, stage III, stage IVa/b and stage IVc).

Methods: Pathologic and clinical features of 303 patients with sporadic MTC, all surgically treated at the Endocrine Surgery Unit and followed at the Endocrine Unit of the University Hospital of Pisa, from 2000 to 2018, were collected. All samples of the primary tumors were re-evaluated by an expert pathologist to be able to characterize high-grade and low-grade tumors according to IMTCGS criteria.

Results: 174/303 (57.4%) patients were female and the median age at diagnosis was 54 (IQR 44-65). According to AJCC 8^th edition, 175 (57.8%) cases were classified in stage I-II, 55 (18.2%) in stage III, 42 (13.9%) in stage IVa/b, and 31 (10.1%) in stage IVc. During a median follow-up of 79 months (IQR 35-133), patients with high-grade tumors showed lower DMFS and LRFS (P < 0.001) than low grade ones. When dividing patients according to stage, high-grade significantly helped to identify those who had lower DMFS and LRFS in stage I-II and III (P < 0.05). However, no differences in DMFS and LRFS between high-grade and low-grade tumors were observed in stage IVa/b cases (p>0.05) Twenty-eight patients (9.2%) died for cancer related causes in a median time of 119 months (IQR 70-165). Patients with high-grade tumors showed a lower DSS (P < 0.001) compared with low-grade. However, when dividing patients according to the initial stage, no difference in DSS were observed between high-grade and low-grade in all the 4 subgroups analyzed (p>0.05)

Conclusions: In our series, the clinical usefulness of grading system in sporadic MTC patients seems to be limited. The presence of distant and latero-cervical lymph nodes metastasis at diagnosis overcomes the prognostic role of grading system for DMFS, LRFS and DSS. Conversely, in lower stages (I, II and III), then with lower risk of recurrence and mortality, patients with high-grade tumors had worst prognosis.