Endocrine Abstracts

Objective: Simultaneous occurrence of MTC and DTC is frequently found. It is unclear whether there is a common pathogenic mechanism. Aim of our study was to characterize clinical features of MTC when coexisting with DTC.

Methods: Of 273 MTC patients followed-up in our department 39 (14.3%) had MTC simultaneously with DTC. They were divided in 4 subgroups according to size. Clinical histopathological data were recorded.

Results: The patients were followed for 1–35 yrs (median:5). Median age at diagnosis was 45 yrs (4–81 yrs). Simultaneous occurrence of distinct MTC-DTC was observed more frequently in patients diagnosed after 2001 compared to earlier (16.7 vs 6.3%, P=0.036). Sex and history of familial disease did not differ. In familial forms of MTC, DTC occurrence was higher in carriers of RET exon 8 (G533C) mutation compared to other RET mutations (17.6 vs 1.8%, P=0.004). Patients with concomitant MTC-DTC had less frequently lymph node infiltration from MTC compared to those with MTC alone (26.3 vs 47.8%, P=0.015), marginally smaller MTC size (median (IQR) 0.9 (1.5) vs 1.2 (1.4) cm, P=0.058) and more often c-cell hyperplasia (58.6 vs 31.5%, P=0.006). No differences were found regarding capsular and soft tissue invasion, multifocality, distant metastases at diagnosis. Stage at diagnosis differed between groups (MTC-DTC vs MTC alone: Stage I+II:71.8 vs 49.8%, III:20.5 vs 27.6%, IV:7.7 vs 22.7%, P=0.007) with the difference remaining significant in both sporadic (P=0.022) and familial MTC (P=0.035). MTC-DTC group had marginally better disease prognosis compared to MTC alone (remission: 67.6 vs 48.7%, stable: 16.2 vs 25.2%, progression: 16.2 vs 26.1%, P=0.05). The 10-year probability of lack of progression of disease did not differ between the two groups. Size of DTC did not seem to affect the clinical course of MTC-DTC.

Conclusions: Simultaneous occurrence of MTC-DTC is occasionally diagnosed. Even though stage at diagnosis is better in MTC-DTC patients, there is no difference in 10-year probability of lack of progression of disease. We report for the first time an increased incidence of DTC in RET exon 8 (G533C) carriers. Whether this mutation-quite common in Greek MTC patients-might participate in shared pathogenic mechanisms needs further investigation.