[Application of 9-gene panel in assisting fine needle aspiration cytology to diagnose thyroid cancer]

Objective: To evaluate the utility of the 9-gene panel as a differential diagnostic method for thyroid nodules within determinate cytological diagnosis and as a parallel diagnostic method for thyroid fine-needle aspiration (FNA) cytology. Methods: 579 liquid-based cytology samples from 544 patients were collected after thyroid FNA diagnosis in our hospital from December 2014 to April 2021. Mutations at any site of 9 genes, namely, BRAF, NRAS, HRAS, KRAS, GNAS, RET, TERT, TP53, and PIK3CA as recorded by the Catalogue of Somatic Mutations in Cancer (COSMIC), were analyzed by next-generation sequencing. Taking postoperative histopathology and cytology results with definite benign or malignant diagnosis as the gold standard, the diagnostic efficacy of the 9-gene panel as a reclassified method for thyroid nodules with indeterminate cytological diagnosis and as a parallel diagnostic method for thyroid FNA cytology were evaluated and compared with that of the BRAF V600E single-gene detection method. Results: Of the 579 thyroid nodules, 196 (33.85%) were Bethesda Ⅱ, 11 (1.90%) were Bethesda Ⅲ, 31 (5.35%) were Bethesda Ⅳ, 27 (4.66%) were Bethesda Ⅴ, and 314 (54.23%) were Bethesda Ⅵ, as diagnosed by thyroid FNA cytology. Among these 579 thyroid nodules, 275 were tested positive for 9-gene mutations, with a mutation rate of 47.5%. Of the 329 thyroid nodules surgically removed, 30 (9.12%) were benign, 5 (1.52%) were borderline, and 294 (89.36%) were malignant. Regarding borderline nodules as malignant nodules, the mutation rates of the 9 genes in the 299 malignant thyroid nodules from high to low were BRAF 62.21% (186/299), NRAS 5.02% (15/299), HRAS 1.00% (3/299), PIK3CA 0.67% (2/299), GNAS 0.67% (2/299), KRAS 0.33% (1/299), TP53 0.33% (1/299), TERT 0.33% (1/299) and RET 0.00% (0/299). The malignant risks of the 9 genes from high to low were BRAF 100% (186/186), PIK3CA 100.00% (2/2), GNAS 100.00% (2/2), TERT 100.00% (1/1), TP53 100.00% (1/1), NRAS 78.95% (15/19), HRAS 75.00% (3/4), and KRAS 50.00% (1/2). For thyroid nodules of Bethesda Ⅲ-Ⅳ (indeterminate diagnosis), the sensitivity (SN) of the 9-gene panel in diagnosing thyroid cancer is 34.48% (10/29), the specificity (SP) is 61.54% (8/13), and the accuracy is 42.86% (18/42); whereas the SN of the BRAF V600E detection method is 0%. Therefore, the diagnostic efficiency of the 9-gene panel is significantly better than that of BRAF V600E single gene detection. For thyroid nodules of Bethesda Ⅱ-Ⅵ, the SN of the 9-gene panel in diagnosing thyroid cancer was 68.83% (254/369), the SP was 90.00% (189/210), the accuracy was 76.51% (443/579), and the area under the curve (AUC) was 0.79; whereas the SN of BRAF V600E single-gene detection in diagnosing thyroid cancer was 63.69% (235/369), the SP was 99.52% (209/210), the accuracy was 76.68% (444/579), and the AUC was 0.82. The SP of BRAF V600E detection is higher than that of the 9-gene panel (P＜0.01), but there is no significant difference in SN, accuracy (both P＞0.05), and AUC (Z=0.85, P=0.396) between them. Gene mutations indicating poor prognosis were detected in 4 nodules of papillary thyroid carcinoma and 1 nodules of follicular thyroid carcinoma, including 2 nodules with TERT and BRAF V600E co-mutations, 1 nodule with TP53 mutation, and 2 nodules with PIK3CA mutation. Conclusions: As a reclassified method for thyroid lesions with indeterminate cytological diagnosis, the 9-gene panel is better than BRAF V600E single gene detection. As a parallel diagnostic method of thyroid FNA cytology, the 9-gene panel has similar diagnostic efficacy as BRAF V600E single-gene detection. The 9-gene panel can detect individual cases with gene mutations indicating poor prognosis. The identification of patients with these special gene mutations has certain implications for the clinical management of them.