In this study, we evaluated the diagnostic accuracy of galectin-3, HBME-1, CK19, HMWCK, cyclin D1, and p27kip1 in the differential diagnosis of thyroid nodules. We found that galectin-3, HBME-1, and CK19 were highly sensitive for DTC, but galectin-3 was the most sensitive and specific.
Galectin-3 has been suggested to be a highly sensitive and reliable diagnostic marker for the preoperative identification of thyroid carcinomas (5
). In a large multicenter study by Bartolazzi et al. (8
), the sensitivity and the specificity of galectin-3 immunodetection in the differential diagnosis of benign and malignant thyroid lesions were higher than 99% and 98%, respectively. Although galectin-3 has been consistently suggested to be a very sensitive marker for papillary carcinoma (5
), some studies revealed that it shows low reactivity in follicular carcinoma (7
). Our study also showed that the expression of galectin-3 was significantly higher in papillary carcinomas than in follicular carcinomas (98.9% vs. 64.0%; p
<0.001). In addition, whereas most of the papillary carcinomas showed diffuse and strong positivity to galectin-3, follicular carcinomas showed focal positivity in 9 (56%) of 16 galectin-3 positive cases, especially in the subcapsular area. Thus, the use of galectin-3 immunohistochemistry in aspiration cytology samples may result in erroneously negative results.
Some recent studies also demonstrated that galectin-3 is highly expressed in benign thyroid lesions and in normal thyroid tissue (11
). The discrepancies in the frequency of galectin-3 immunoreactivity in benign lesions may be related to the different antibody detection systems and the cut-off values for positive and negative staining. In the thyroid gland, endogenous biotin is invariably expressed in thyrocytes, mostly in Hurthle cells. Thus, a biotin-based detection system may provide false positive results. It has been suggested that galectin-3 immunodetection may be a useful adjunct in the distinction between benign and malignant thyroid tumors, only if performed in a biotin-free detection system (9
Besides galectin-3, several markers have been investigated as useful markers for the diagnosis of thyroid carcinoma. HBME-1 has been reported to be one of the most promising markers (11
). HBME-1 seems to be a sensitive marker for thyroid carcinoma, especially in follicular carcinoma. In our study, it was expressed in 88% of follicular carcinomas, compared with the 64% positivity for galectin-3. However, HBME-1 was also expressed in 48.6% of follicular adenomas and 20.4% of nodular hyperplasias, these frequencies being similar or slightly higher than those previously reported (12
). Thus, although HBME-1 contributes to the diagnosis of DTC, it cannot be applied in the preoperative or differential diagnosis of follicular-patterned lesions due to its low specificity.
CK19 has been reported to be strongly and diffusely expressed in papillary carcinoma, whereas it is usually absent or focally expressed in follicular carcinoma and benign nodules (11
). In our cases, almost all papillary carcinomas including follicular variants of papillary carcinoma showed strong and diffuse CK19 immunoreactivity. However, our nodular hyperplasias, follicular adenomas, and follicular carcinomas also showed CK19 immunoreactivity in 9.3%, 28.6%, and 44.0% of cases, respectively, and 20% of follicular carcinomas and 11% of follicular adenomas showed diffuse staining for CK19, although the staining was less intense than that observed in the papillary carcinoma. It is hard to make any generalizations about the expression of CK19 in follicular lesions due to the relative paucity of cases studied, as most of the previous studies on CK19 expression in thyroid nodules have targeted papillary carcinomas, and the extent of CK19 immunoreactivity in follicular lesions in the previous studies is quite variable. The CK19 immunoreactivity of follicular adenoma in our study was higher than that previously reported. However, Sahoo et al. (22
) reported that 25% of their follicular adenomas showed extensive immunoreactivity for CK19 (2+ in 1, 3+ in 4 of 20 follicular adenomas), and Miettinen et al. (21
) also reported that 24% of follicular adenomas and 59% of follicular carcinomas showed CK19 reactivity in >10% of lesions, suggesting that CK19 patterns are not reliable in the differentiation between papillary carcinomas and follicular neoplasms. Thus, although the immunoreactivity for CK19 is more frequent and more diffuse in papillary carcinoma, its immunoreactivity in follicular lesions may limit its utility as a diagnostic marker. HMWCK expression was patchy but strong in 59.7% of papillary carcinomas, and its staining was less frequent in follicular variants of papillary carcinoma, being expressed in 35.3%. HMWCK seems to be a highly specific marker for papillary carcinoma; however, its low sensitivity limits its use in diagnosis.
We attempted to identify a combination of markers with the greatest diagnostic accuracy. Nikiforova et al. (30
) reported that follicular carcinoma with PAX-PPARγ rearrangement showed immunoreactivity for galectin-3 but not for HBME-1 and that those with RAS mutations displayed HBME-1-positive/galectin-3-negative immunophenotype. Thus, we thought that HBME-1 would complement the low sensitivity of galectin-3 in the diagnosis of follicular carcinoma, and found that all carcinomas were positive for either galectin-3 or HBME-1. An immunohistochemical diagnostic panel comprising these markers increased the sensitivity for DTC to 100%. However, its specificity for DTC was lowered to 65.2%. When we examined the co-expression of galectin-3 and HBME-1 or galectin-3 and CK19 as a possible marker of DTC, we found that it was the most specific and accurate marker with 100% specificity and 95.3% diagnostic accuracy. Although this combined use of HBME-1 and CK19 with galectin-3 cannot increase the sensitivity in the diagnosis of DTC, it can discriminate galectin-3-positive benign lesions from galectin-3-positive thyroid carcinomas and thus increase the specificity.
In our study, the overexpression of cyclin D1 and loss of p27kip1
were associated with DTC. Their expression was much higher in papillary carcinomas than in follicular carcinomas, and there was no difference in expression between follicular carcinomas and follicular adenomas. There have been a few reports demonstrating that cyclin D1 and p27kip1
immunostaining varies according to tumor phenotype (24
). However, in our study, their sensitivity and specificity for DTC or papillary carcinoma was relatively lower than for the other markers and thus, were not useful in distinguishing between benign and malignant thyroid nodules or between papillary carcinoma and follicular carcinoma.
In summary, galectin-3 is a useful marker in the distinction of benign and malignant thyroid tumors, and the combined use of HBME-1 and CK19 can increase the specificity and diagnostic accuracy. Galectin-3 and HBME-1 can be used as adjuncts for the differential diagnosis of follicular neoplasms, although the low sensitivity of galectin-3 and the low specificity of HBME-1 for the diagnosis of follicular carcinoma should be born in mind. In addition, CK19 and HMWCK can aid in the diagnosis of papillary carcinoma; however, the low specificity of CK19 and low sensitivity of HMWCK may limit their utility.