Introduction: Recently, small medullary thyroid carcinomas (sMTCs) (≤1.5 cm) are frequently diagnosed, occasionally as incidental findings in surgical and autopsy specimens. Their clinical course varies. We examined whether tumor size is a predictor of clinical behavior.
Patients and methods: One hundred and one sMTC patients (36.6% males, 47.1% familial) followed-up for 0.935 years. Patients were classified according to tumor size (cm) in group1: 0.10.5 (n=25), group2: 0.60.8 (n=22), group3: 0.81.0 (n=23), group4: 1.11.5 (n=31).
Results: Familial cases did not differ from sporadic ones concerning stage at diagnosis or outcome. Preoperative and postoperative calcitonin levels were positively associated with tumour size (P<0.001). At diagnosis, capsular and lymph node invasion were more frequent in groups 3 and 4 (P<0.022, P<0.001 respectively). The stage at diagnosis was more advanced and the outcome less favourable with increasing tumour size (P<0.004). Group 1 and 2 patients were more frequently cured (group 1: 88%, group 2: 86.7%, group 3: 72.7%, group 4: 51.7%, P=0.009). The 10-year probability of lack of progression of disease according to tumour size did not differ significantly between the four groups (group 1: 96%, group 2: 100%, group 3: 100%, group 4: 81.5%, x2=4.61, P=0.2, log rank); it differed marginally between patients with tumour 0.11.0 and 1.11.5 cm (98.5 and 81.5%, x2=4.15, P=0.042, log rank). In the subgroup of microMTCs (≤1.0 cm) patients with microMTC ≤0.8 had less advanced stage at diagnosis compared to 0.91.0 cm (stage I and II: 89.4 vs 66.7%, stage III: 8.5 vs 33.3% and stage IV: 2.1 vs 0%, P=0.032). No differences in the outcome were found between microMTC subgroups.
Conclusion: The probability of 10-year disease progression slightly increases in >1.0 cm sMTCs. In microMTCs although the stage is less advanced in microMTCs≤0.8 cm, the outcome is similar to larger microMTs (0.91.0 cm). Thus tumor size may be of clinical importance only in patients with MTCs >1 cm.