This study included 94 patients with intermediate-to-high recurrence risk in PTC, with a male-to-female ratio of 1:1.35. The mean age was 43.99 ± 15.35 years, and the average follow-up time was 1.90 ± 1.75 years. No distant metastases were detected in patients during diagnosis or follow-up. Among these patients, 88 (93.62%) patients exhibited at least one genetic alteration. 78 (82.98%) patients had gene mutations, 11 (11.70%) patients had gene fusions, 1 (1.06%) patient had both gene mutation and fusion, and 6 (6.38%) patients showed no genetic abnormalities. The gene mutation events observed included BRAF V600E missense mutation (n = 75), TERT promoter mutation (n = 17), AKT1 missense mutation (n = 1), KRAS missense mutation (n = 1), TP53 missense mutation (n = 1), PIK3CA missense mutation (n = 2), and HRAS missense mutation (n = 1). The gene fusion events observed in this study included CCDC6-RET gene fusion (n = 7), NCOA4-RET gene fusion (n = 2), and ETV6-NTRK3 gene fusion (n = 2).

Association between AF of BRAF V600E mutation and gender/age

The BRAF V600E mutation occurred in 75 cases (76.5%) of PTC patients, with a male-to-female ratio of 1:1.27. The average age was (44.89 ± 15.03) years, and the mean BRAF V600E mutation AF was (19.36 ± 11.27) %. For males, the average of AF was (19.09 ± 10.60%), and for females, it was (19.58 ± 11.89%). The difference in BRAF V600E mutation AF between males and females was not statistically significant (p = 0.87). The age distribution of average BRAF mutation frequency is shown in Table 2, and the trend is illustrated in Fig. 1, indicating a rise-fall-rise pattern with peaks at ages 30–39 years and 70–79 years groups. According to ATA and AJCC guidelines [13], age 55 is a critical point for AJCC staging. Therefore, the study population was divided into ≥ 55 years and < 55 years groups, showing no statistically significant difference in BRAF mutation AF between the two groups (p = 0.28).

Table 2 Average BRAF V600E Mutation AF Across Different Age Groups (n = 75)Fig. 1

Line chart of AF of BRAF V600E mutation/Age (n = 75)

Association between AF of BRAF V600E mutation and extrathyroidal extension

Among PTC patients with BRAF V600E mutations, 18 cases (24%) showed extrathyroidal extension breaking the thyroid capsule, as shown in Table 3. The line graph in Fig. 2 shows the relationship between the number of cases with thyroid cancer invasion and the BRAF V600E mutation AF. A significant association was found between extrathyroidal extension and the increased AF of BRAF V600E mutation. (p = 0.002, OR = 1.100, OR (95%CI) = 1.037–1.166).

Table 3 Clinical Characteristics Across Different BRAF V600E Mutation AF (n = 75)Fig. 2

Line chart of BRAF percentage of double/multiple loci mutations, percentage of recurrence, percentage of extrathyroidal extension (n = 75)

Association between AF of BRAF V600E mutation and recurrence

Among PTC patients with BRAF mutations, 10 cases (13.3%) experienced recurrence, as shown in Table 3, with an average follow-up time of (1.86 ± 1.26) years. A significant association was found between BRAF V600E mutation AF and thyroid cancer recurrence (p = 0.023, OR = 10.080, OR (95%CI) = 1.010–1.154). Figure 2 shows the line graph depicting the recurrence rate/BRAF V600E mutation AF. The receiver operating characteristic (ROC) curve was created using sensitivity on the y-axis and (1-specificity) on the x-axis. The area under the curve (AUC) was 0.717 (95% CI = 0.541–0.893), as shown in Fig. 3. The point with the highest Youden index was at a BRAF V600E mutation AF of 28.2% (sensitivity = 60.0%, specificity = 80.0%, Youden index = 0.40, accuracy=77.3%), as shown in Table 4. Table 5 shows that the risk of thyroid cancer recurrence is six times higher with a BRAF V600E mutation AF > 28.2% compared to AF ≤ 28.2%.

Fig. 3

The ROC Curve for Predicting Recurrence Based on BRAF V600E Mutation AF (n = 75)

Table 4 Sensitivity and specificity of BRAF V600E mutation AF for predicting recurrence at various cutoff values (n = 75)Table 5 Binary Logistic Regression Analysis of BRAF V600E Mutation AF > 28.2% and recurrence risk (n = 75)Association between AF of BRAF V600E mutation and combination with double/multiple loci mutations

Among PTC patients with BRAF mutations, 14 cases (18.67%) exhibited double/multiple loci mutations. These included 11 cases with BRAF + TERT mutations, 1 case with BRAF + KRAS mutation, 1 case with BRAF + TERT + PIK3CA mutations, and 1 case with BRAF + TERT + AKT1 mutations. The likelihood of double/multiple mutations significantly increased with the elevated BRAF gene mutation frequency (p = 0.006, OR = 1.088, OR (95%CI) = 1.024–1.156), as shown in Fig. 2, which depicts the relationship with BRAF V600E mutation AF. Compared to the group with a single BRAF mutation, the group with combined double/multiple BRAF mutations had a higher recurrence rate (p = 0.019, OR = 10.687, OR (95%CI) = 2.468–46.282), and a higher incidence of thyroid cancer breaking through the thyroid capsule (p < 0.001, OR = 16.562, OR (95%CI) = 4.178–65.662), as shown in Table 6.

Table 6 BRAF monoallelic mutation group Versus BRAF combined with other mutations group (n = 75)Association between AF of TERT mutation and clinical statistics

TERT promoter mutations were present in 17 cases (17.3%) of PTC patients, with a gender ratio of 1:1.13 and an average age of (61.41 ± 10.86) years. The average TERT mutation frequency was (46.71 ± 11.09) %, and all mutations were C228T missense mutation. As shown in Table 7, 1 patient had a single-point mutation, 13 patients had double-point mutations, 2 patients had triple-point mutations, and 1 patient had a TERT gene mutation combined with ETV6-NTRK3 gene fusion. 7 patients (41.18%) experienced recurrence with a mean follow-up of (2.65 ± 5.17) years. Patients who experienced recurrence all had TERT mutation frequencies greater than 45%. There were no statistically significant differences in TERT mutation AF between different genders and age groups. Increasing BRAF V600E mutation AF leading to a significant increase in TERT mutations (p = 0.002, OR = 1.116, OR (95%CI) = 1.042–1.197). Patients with TERT mutations have a significantly higher recurrence rate (p < 0.001, OR = 12.429, OR (95%CI) = 2.805–55.064) and an increased risk of tumor breakthrough of the capsule (p < 0.001, OR = 22.500, OR (95%CI) = 5.078–99.696), as shown in Table 8. There were no clear statistically significant differences in gender, age, thyroid capsule penetration, and recurrence among different AF of TERT mutation.

Table 7 TERT mutation types (n = 17)Table 8 BRAF monoallelic mutation group Versus BRAF + TERT mutations group (n = 75)Gene fusion

11 cases (11.22%) were detected with gene fusions, with a sex ratio of 1:1.75 and a mean age of (38.09 ± 16.15) years. The gene fusions included 7 cases of CCDC6-RET fusion, 2 cases of NCOA4-RET fusion, and 2 cases of ETV6-NTRK3 fusion, as shown in Table 9. The CCDC6-RET fusion was found on chromosome 10, involving exon E1:E12 fusion. The NCOA4-RET fusion was found on chromosome 10, involving exon E8:E12 fusion. The ETV6-NTRK3 fusion was found on chromosomes 12 and 15, involving exon E4:E14 fusion. The remaining 10 cases did not exhibit any combined gene mutations. Out of the 11 cases of gene fusion patients with papillary thyroid carcinoma, only one case showed a combination of ETV6-NTRK3 fusion and TERT mutation. Among the gene fusion patients, two cases of NCOA4-RET fusion were of the Diffuse Sclerosing Variant of Papillary Thyroid Carcinoma (DSVPTC). Additionally, one patient with ETV6-NTRK3 gene fusion experienced recurrence.

Table 9 Clinical characteristics of patients with gene fusion (n = 11)Figures, tables and schemes