Risk Factors For Affecting Radioactive ¹³¹I Remnant Ablation And Prognosis In Patients With Papillary Thyroid Microcarcinoma

ObjectivePapillary thyroid microcarcinoma?PTMC?is defined as tumor with diameter less than or equal to 1cm according to the World Health Organization?WHO?.PTMC has a good prognosis and long-term disease-free survival rate.However,some patients may recurrent after treatment.Radioactive ¹3131 I remnant ablation?RRA?is an important adjuvant treatment for differentiated thyroid carcinoma.Identify the risk factors that affect RRA and prognosis of PTMC is expected to direct the selection of treatment.In this study we aimed to analyzed the risk factors for affecting RRA and prognosis in patients with papillary thyroid microcarcinoma.MethodsThis study retrospectively analyzed 231 patients with PTMC who met the inclusion criteria and referred to our hospital for their first RRA during the period of January 2011through April 2018.The mean age of the patients was 47.23±11.45 years?range,23 to74?.The male:female ratio was 1:2.45.All patients underwent total?208?or near total?23?thyroidectomy.And except for 4 patients,all the patients were performed prophylactic or therapeutic central lymph node dissection.RRA was given at least 4-6weeks after thyroidectomy.The ablative dosage of ¹³¹I was 2.7-9.2GMq?75-250mCi?.¹³¹I whole-body scan?WBS?was performed 4 to 7 days later.Repeat treatment was given with interval of 6 months if need.Patients were classified as clinical cure status and non-clinical cure status according to the thyroglobulin?Tg?under thyroid-stimulating hormone?TSH?suppression therapy 6-12 months after RRA,WBS after RRA and other imaging examination results.Clinical cure status was defined if there was no adioactive concentration except in thyroid bed,Tg was<0.2ng/L, thyroglobulin antibody?Tgab?was negative and no evidence of disease on cervical ultrasound,CT,MRI,and PET/CT.Patients were re-examined every 2 months within 6months after RRA,and every 6-12 months 6 months later.Patients were followed up by telephone and outpatient visits.Median follow up period was 39 months?range,8 to 95?.And patients were classified as non-structural recurrence status and structural recurrence or disease persistent status.Structural recurrence and disease persistence refer to new lesions or lesions becoming larger after half a year of ¹³¹I treatment,ie,patients with unsatisfactory or progressive structural outcomes in the 2015 ATA guidelines for dynamic efficacy assessment.The factors that affect the efficacy of RRA and recurrence/disease persistent were analyzed.Results1.168 patients?72.73%?were in clinical cure status and 63 patients?27.27%?were not after the first RRA.Univariate analysis showed that age?t=2.643,P=0.009?,primary tumor size?z=-2.164,P=0.030?,the number of central lymph node metastasis?z=-2.777,P=0.005?,metastatic central lymph node/harvested central lymph node?z=-3.586,P<0.005?,the number of lateral lymph node metastasis?z=-2.180,P=0.029?,metastatic lateral lymph node/harvested central lymph node?z=-2.359,P=0.018?,TNM stage?X²=10.184,P=0.009?,accompanying hashimoto's thyroiditis?X²=9.070,P=0.003?,TSH?X²=7.910,P=0.04?and pre-ablation Tg?z=-9.155,P<0.005?were significantly related to clinical cure rate.2.By the receiver operating characteristic curve?ROC?,the cutoff values of pre-ablation Tg to predict a clinical cure status was 4.36ng/L with a area under the curve?AUC?of0.891,a sensitivity of 81.4%and a specificity of 79.2%.And the cutoff values of primary tumor size was 0.425cm but with low diagnostic capacity.The AUC was 0.592.On multivariate analysis,primary tumor size,TNM stage,and pre-ablation Tg were significant.Primary tumor size>0.425cm?OR=6.069,P=0.035?,TNM stage??OR=40.878,P=0.03?and pre-ablation Tg>4.36 ng/L?OR=21.690,P=0.004?were significantly associated with non-clinical cure status.3.Median follow up period was 39 months?range,8 to 95?.11 patients had recurrence,and the recurrence rate was 4.26%.All patients had cervical lymph node recurrence and the average time to recurrence was 26 months after surgery.3 patients were disease persistent status.Three patients died of thyroid cancer non-related disease,and the disease-specific survival rate was 100%.TNM stages??RR=2.193,P=0.096?,pre-ablation Tg?RR=1.066,P=<0.009?and non-clinical cure status after first RRA?RR=3.602,P=0.048?were associated with recurrence or disease persistent status by univariate Cox regression analysis.The cutoff values of pre-ablation Tg to predict a recurrence or disease persistent status was 8.515ng/L.4.Kaplan–Meier curves showed different disease free survival rates in clinical cure status versus non-clinical cure status?log rank=9.530,P=0.002?,pre-ablation Tg>8.515ng/L versus pre-ablation Tg?8.515 ng/L?log rank=19.796,P<0.005?,TNM stages?versus??log rank=96.519,P<0.005?.5.Pre-ablation Tg>8.515ng/L,TNM stages?were the independent prognostic variable that predicted recurrence or disease persistent status by multivariate Cox regression analysis?RR=9.76,P<0.005;RR=17.78,P=0.001?.ConclusionsThe clinical cure rate of PTMC after first RRA was excellent.Primary tumor size>0.425cm,TNM stage?and pre-ablation Tg>4.36 ng/L were significantly associated with non-clinical cure status.PTMC has a good prognosis and the recurrence rate was very low after RRA.Pre-ablation Tg,TNM stages?were the independent prognostic variable that predicted recurrence or disease persistent status.The patients with ps-Tg>8.515ng/L,TNM stages?require more intensive treatments.