The differences between unilateral multifocality and bilateral multifocality in papillary thyroid carcinoma: a retrospective cohort study

Background: The differences between unilateral multifocality and bilaterality in papillary thyroid carcinoma (PTC) are not fully understood. This study aimed to investigate the differences between unilateral multifocal PTC (UMPTC) and bilateral multifocal PTC (BMPTC).

Methods: Retrospective data analysis was done on 503 individuals who underwent complete thyroidectomy for PTC. Patients were classified into subgroups according to the type of multifocality including the UMPTC and the BMPTC. The relationships of demographic and clinicopathological features among these groups were analyzed.

Results: The patients were divided into the UMPTC group (n=117) and the BMPTC group (n=386). Among them, the BMPTC group was further divided into the N1-BMPTC group (261 cases with one lesion on each thyroid lobe) and the N2-BMPTC group (125 cases with one or more lesions on one lobe and two or more lesions on the other lobe). The maximum tumor diameter (MTD), in the BMPTC group, N1-BMPTC group, and N2-BMPTC group were larger than that in the UMPTC group. The recurrence rate of the N1-BMPTC group was higher than that of the UMPTC group. There were no significant differences in other clinicopathological characteristics [gender, age, body mass index (BMI), presence of Hashimoto's thyroiditis, presence of thyroid nodules, occurrence of capsular invasion, occurrence of extrathyroidal extension, occurrence of lymph node metastasis, and the American Joint Committee on Cancer (AJCC) staging]. The N1-BMPTC group was associated with lymph node metastasis and tumor recurrence. In addition, the disease-free survival (DFS) rates showed the N1-BMPTC group having the lowest DFS rate among the UMPTC, N1-BMPTC, and N2-BMPTC groups.

Conclusions: Patients with N1-BMPTCs have a higher recurrence rate than those with other kinds of multifocal PTC.