Cytological evaluation of FNAB represents the gold standard technique for the diagnosis of CLN suspected to harbor metastatic disease from thyroid cancer as well as from other primary tumors. The technique accuracy, highly dependent on the experience and ability of the cytopathologist, has been reported to vary from 73% to 94% [17, 18, 22, 25]. Over the last years, following clinical evidence showing that FNAB-Tgp in fine-needle washout improves the accuracy of FNAB-C in the evaluation of CLN metastases of DTC, it has been recommended the routine association of FNAB-Tgp with FNAB-C in the preoperative diagnosis of suspicious CLN [6, 7, 14–27, 33]. We here report our experience with 35 CLN for which a definitive diagnosis was available, including cases harboring metastases from PTC, MTC, ATC and other primary tumors.
The results showed that, on 32 CLN harboring metastases from papillary and anaplastic thyroid carcinomas, FNAB-C had 88.5% accuracy, that is within the range reported in other studies [17, 18, 22, 25]. When FNAB-Tgp and FNAB-Tgm were used singly they had a diagnostic performance comparable and not statistically different from that of FNAB-C. In addition, the combination of FNAB-Tgp and/or FNAB-Tgm with FNAB-C did not improve significantly the diagnostic value of FNAB-C. On the other hand, both FNAB-Tgp and FNAB-Tgm compared favorably with FNAB-C. As expected, a major disagreement among the three diagnostic tests was observed in the 3 CLN harboring metastasis from ATC (Table 2, CLN number 10, 12 and 13). It is worth to note that although ATC are undifferentiated cancers, i.e. devoid of thyroid specific gene expression, we consider the absence or the low level (below the cut-off value of 1 ng/FNAB) of Tgp or the absence of Tgm as false negative results. In fact, in one of the three metastatic CLN from ATC the detectable Tgp correctly diagnosed one of them (CLN number 13), and the detectable Tgm was diagnostic in the other two (CLN number 10 and 12).
A major diagnostic value of FNAB-Tgp and FNAB-Tgm was observed in cases of uninformative FNAB-C, given that in all 3 CLN characterized by inadequate cytology FNAB-Tgp provided the correct diagnosis. In these cases, FNAB-Tgm also provided the correct diagnosis in 2 of them, being inadequate in one. Other instances in which the combined use of FNAB-Tgp, FNAB-Tgm and FNAB-CTm is valuable include those cases in which FNAB-C diagnosis is not consistent with patient’s clinical and biochemical parameters. This was the case (Table 1, CLN number 19 and 20) of the patient harboring metastatic MTC and characterized by elevated level of serum calcitonin in which FNAB-C indicated metastatic PTC, while on the contrary both FNAB-Tgp and FNAB-Tgm were negative, and FNAB-CTm positive.