Determination of factors affecting prognosis and recurrence risk in patients with papillary thyroid microcarcinoma

The incidence of papillary thyroid microcarcinoma (PTMC) has increased dramatically in the last decade in Turkey and all over the world. Most of these tumors are indolent, showing progression less frequently. However, PTMCs with certain clinical and histopathological features have a higher risk of recurrence and poor prognosis despite treatment. This retrospective, case-control study aims to examine the risk factors and treatment strategies that affect the prognosis and recurrence risk in PTMC. A total of 302 patients diagnosed and followed up with PTMC by the Endocrinology and Metabolism Department of Baskent University Faculty of Medicine between January 2011 and December 2021 were enrolled in this study. Recurrence was defined as the presence of lymph node metastasis (LNM), recurrent mass or distant metastasis on USG and whole body scintigraphy scan of patients who were followed up in remission for at least 6 months. Patients were classified according to TNM 2018 staging system and categorized according to American Thyroid Association (ATA) 2015 risk stratification. Relapsed and non-relapsed patient groups were compared in terms of demographic characteristics, histopathological and clinical features, laboratory findings, surgery data, whether radioactive iodine treatment was given, dose and number of courses administered. Radioactive iodine administration was also evaluated and both groups were compared in terms of clinical anf pathologic features. At the end of a mean follow-up period of 51 months, recurrence was detected in 4 (1.3%) of the patients. All of the patients with recurrence were accepted as intermediate risk according to the ATA 2015 risk stratification. Data showed that lymph node metastasis at the time of diagnosis (p=0.001), type of surgery (p=0.012), surgical margin positivity (p=0.008), being in the intermediate risk group according to ATA risk stratification (p=0.001), were found to be significantly associated with prognosis and risk of recurrence in PTMC. Tumor size, bilaterality, multifocality, presence of vascular, capsular and extrathyroidal invasion were not associated with recurrence. When we evaluated the experience of our center in the application of radioactive iodine (RAI) ablation in the postoperative period, PTMC patients who received RAI treatment were found to be younger (p=0.003) with larger tumor size (p<0.001), demonstrating higher rates of multifocality (p<0.001), bilaterality (p<0.001),capsule (p<0.001), vascular (p=0.003), and extrathyroidal invasion (p=0.012), surgical margin positivity (p=0.01), LNM at the time of diagnosis (p=0.05) when compared with patients who didn't receive RAI treatment. They were also observed to be at higher risk according to ATA risk stratification (p<0.001) and at a more advanced stage (p=0.012) according to TNM classification in comparison. PTMC has low recurrence rates and has a good prognosis. Presence of lymph node metastases at the time of diagnosis, surgical margin positivity and ATA risk classification were found to be effective in determining the risk of recurrence. The presence of these risk factors indicates the need for a more aggressive treatment approach and a closer follow-up regime. In addition, it was thought that the radioactive iodine treatment indications were determined by pathologic features of the tumor. Therefore, the number of reccurent tumors may have been found to be low. Considering the risk factors identified in our study, more comprehensive studies are still needed to determine these risk factors, treatment strategies and RAI indications for PTMC patients. Key words: Papillary thyroid microcarcinoma, Prognosis, Recurrence, Radioactive iodine ablation