Multifocality and bilaterality in medullary thyroid cancer: basis for a proof-of-concept safety of lobectomy.

Objective: At present, total thyroidectomy and central neck dissection are the surgical approaches recommended for the initial treatment of medullary thyroid cancer (MTC) independently of the size, number of tumor foci, age of patients, and other demographic and clinico-pathological parameters. The aims of the present study were to assess the prevalence of multifocality in hereditary (hMTC) and sporadic (sMTC) patients and to correlate the presence of multifocality with clinico-pathological parameters to provide a proof of concept that lobectomy can be safely performed in selected cases. Methods: We analyzed the epidemiological, pathological, and clinical data of 389 MTC (311 sMTC and 78 hMTC) diagnosed in our center from 2005 to 2018. Results: Multifocality was found in 89/389 cases (22.9%), (45/311 (14.5%) sMTC and 44/78 (56.4%) hMTC). Bilaterality was detected in 27/311 (8.7%) of all sMTC, particularly in 27/45 (60%) of multifocal ones, and in 44/78 of hMTC (56.4%). Multifocality was correlated with a more aggressive phenotype in both sMTC and hMTC, and the multivariate analysis showed that it was statistically and independently associated with tumoral extrathyroidal extension and N1 status in sMTC and with N1 status and persistent disease in hMTC. However, none of the presurgical factors could predict the presence of both multifocality and bilaterality. Conclusions: Our study demonstrated that the rarity of multifocality and, in particular, of bilaterality, in sMTC represents the proof of concept for considering a more conservative surgical approach in selected sMTC cases. This approach cannot be considered in hMTC due to the high prevalence of multifocal and bilateral cases.