Active surveillance for young patients with insular thyroid cancer: an initial and novel finding.

Insular thyroid cancer (ITC) is a relatively rare thyroid malignancy that has an unclear prognosis. Recent studies have indicated that watchful waiting is sufficient for younger patients with more differentiated thyroid lesions such as papillary thyroid microcarcinoma (PTMC). In this study, we investigated the prognosis of younger patients (< 45 and < 55 years old) with ITC and compared their outcomes to patients with PTMC and follicular thyroid microcarcinoma (FTMC). We hypothesized that ITC, like PTMC and FTMC, can be managed with active surveillance in younger patients with this disease. We investigated a large cohort of younger patients with ITC, PTMC, or FTMC who were listed in the Surveillance, Epidemiology, and End Results database between 2004 and 2013. Patient mortality was examined by Kaplan-Meier analyses with log-rank tests and Cox proportional hazards regression analyses. In the study cohort, the rate of cancer-specific mortality per 1000 person-years for younger ITC patients (< 45 and < 55 years) was lower than that for PTMC and FTMC. Kaplan-Meier analyses revealed that the cancer-specific and all-cause mortality rates in younger ITC patients were similar to those of PTMC and FTMC. Similar results were obtained when cases with tumor extension were excluded from the analysis. The unanticipated excellent prognosis of younger patients with ITC challenges the current clinical practice of automatically treating this disease, and offers new implications for management such as pursuing active surveillance instead.