Synergic effects of histology subtype, lymph node metastasis, and distant metastasis on prognosis in differentiated...

Differentiated thyroid carcinoma (DTC) is the most common clinical type of thyroid carcinoma. There are rare reports on the synergic effects of the different clinicopathological risk factors on the prognosis of it.

We retrospectively reviewed data on 86,032 DTC patients from the Surveillance, Epidemiology, and End Results (SEER) database. Univariate and multivariate Cox regression analyses were conducted to evaluate the correlation between clinicopathological factors and the prognosis of DTC. Relative excess risk (RERI) of synergic effect, attributable proportion (AP) of synergic effect, and synergy index (SI) were calculated to assess synergic effects. Kaplan-Meier analyses with log-rank tests was used to plot the survival curve affected by different risk factors.

Histology subtype, lymph node metastasis (LNM) status, and distant metastasis (DM) were independent risk factors for cancer-specific survival (CSS) and all-cause survival (ACS) in the multivariate analysis (all, P<0.001). Patients' age at diagnosis, sex, extrathyroidal extension, and radiation also influenced prognosis (all, P<0.001). The cancer-specific mortality (CSM) and all-cause mortality (ACM) rates per 1,000 person-years were higher in patients with follicular thyroid carcinoma (FTC) and in those with N1 stage and M1 stage disease. Furthermore, we observed a significant synergic effect between histology subtype and N stage, as well as histology subtype and M stage for the CSM of DTC (RERI =48.806, AP =0.853, SI =7.565; RERI =37.889, AP =0.430, SI =1.771, respectively). However, no synergic effect was observed in the case of the N stage and M stage for the CSM of DTC (RERI =7.928, AP =0.084, SI =1.093).

Patients with histology subtype of FTC and N1 stage, histology subtype of FTC and M1 stage had significant additive synergic effects on DTC prognosis for CSM.