Objective:To explore the clinical pathological characteristics and initial 131I curative responses of familial differentiated thyroid cancer (FDTC) and sporadic differentiated thyroid cancer (SDTC). Methods:A total of 66 FDTC patients (19 males, 47 females, age (39.8±11.7) years) and 1 701 SDTC patients (442 males, 1 259 females, age (40.9±11.3) years) who underwent 131I therapy in Department of Nuclear Medicine, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology between January 2010 and August 2018 were retrospectively enrolled. The clinical pathological characteristics, preablative stimulated thyroglobulin (ps-Tg), preablative stimulated thyroglobulin antibody (ps-TgAb) and response to initial therapy (excellent response, indeterminate response, biochemical incomplete response, structural incomplete response) of two groups were analyzed and compared. The clinical pathological parameters included age, gender, pathological type, tumour maximum diameter, bilateral, multifoci, nodules goiter, thyroiditis, thyroid membrane invasion, lymph node metastasis (LNM), invasion of the surrounding soft tissues, distant metastasis, TNM staging and American Thyroid Association (ATA) risk stratification (low-risk, intermediate-risk, high-risk). χ2 test or Fisher exact test and independent-sample t test were used to compare the data between two groups. Results:Comparing with SDTC group, FDTC group showed higher proportion of bilateral foci (45.5%(30/66) vs 31.2%(530/1 701); χ2=5.999, P=0.010), thyroid membrane invasion (43.9%(29/66) vs 26.6%(452/1 701); χ2=9.672, P=0.002) and distant metastasis (15.2%(10/66) vs 6.2%(105/1 701); χ2=8.418, P=0.004). There was a statistical difference in risk stratification between two groups (high-risk: 18.2%(12/66) vs 9.2%(156/1 701); intermediate-risk: 68.2%(45/66) vs 72.7%(1 237/1 701); low-risk: 13.6%(9/66) vs 18.1%(308/1 701); χ2=6.898, P=0.030). But the tumor maximum diameter of FDTC group was smaller than that of SDTC group ((1.24±0.74) vs (1.50±0.92) cm; t=-2.275, P=0.020). There were no significant differences in other clinical pathological parameters between FDTC group and SDTC group ( t=-0.804, χ2 values: 0.101-5.359, all P>0.05). There were no significant differences between two groups in the postoperation ps-Tg, ps-TgAb levels and the response to initial therapy after 131I treatment ( χ2 values: 0.059-1.915, all P>0.05). Conclusions:The FDTC group displays distinct characteristics as increased aggressiveness at diagnosis. But after accurately treatment, there is no significant difference in the response to therapy between two groups.