A striking difference was found regarding the proportion of positive cells for TTF-1 and napsin A in cases of AC. Reactivity in >50% of the tumor cells was found in only two of eight and seven of 10 positive cases of TTF-1 and napsin A, respectively (Table 1).
Sensitivity, specificity, and diagnostic positive predictive value of the three markers are summarized in Table 2.
Until recently, the differentiation of NSCLC variants had an academic but not a therapeutic implication, because all were treated according to similar strategies (Schrump et al., 2008). Bevacizumab, when combined with carboplatin and paclitaxel, improves the overall survival in patients with advanced or recurrent NSCLC. However, this drug is not recommended in patients with SCC or neoplasms with a dominant squamous component (Cohen and Weydert, 2011). In certain patients, the distinction of squamous and non-SCC including AC and LCC cannot be made by the assessment of morphology alone. In this situation, immunohistochemical markers may provide additional diagnostic information, especially in small biopsy and cytologic materials (Stoll et al., 2010; Travis et al., 2010).
Previous studies have been performed to evaluate the usefulness of p63 for the distinction of primary pulmonary SCC. The results of Wu et al. (2003), Au et al. (2004), and Kargi et al. (2007), who used formalin-fixed, paraffin-embedded tissue sections, revealed p63 positivity in between 81 and 100% of NSCLC with squamous differentiation. Similar results were obtained by Jorda et al. (2009) and Kalhor et al. (2006) using cytologic material. They observed a positive expression in 88 and 100% of SCCs, respectively. The results of the current study were consistent with the previous studies as 12 of 14 SCCs reacted with p63, reflecting the high sensitivity of this marker (85.7%). Although the two well-differentiated SCCs were negative, all poorly differentiated SCCs showed a strong and diffuse reactivity of most tumor cells. This result confirmed that p63 is a promising marker to indicate a minimal squamous differentiation as reported by Shimada et al. (2009). However, p63 positivity in pulmonary tumors is not limited to SCCs. For ACs, Wang et al. (2002) reported a p63 positivity in 65% of the cases but in a focal pattern in contrast to the diffuse staining in poorly differentiated SCCs. Other investigators have shown considerably lower percentages of p63-positive pulmonary ACs ranging in most studies from 12.1 to 18.3% (Lim et al., 2003; Massion et al., 2003; Sheikh et al., 2004). In other studies, p63 was not detected in any of the ACs (Kargi et al., 2007). This discrepancy in p63 expression could be related to differences in the techniques used and variations in the antibody dilutions used in different studies (Au et al., 2004).
These results are largely in accordance with those of the present study. Only one of 12 (8.3%) ACs was weak and focally (11–50%) positive for p63 whereas all LCCs were nonreactive, indicating a high specificity of this marker for SCC (93.8%). Therefore, several approaches have been proposed to improve the subtyping of NSCLCs, including the use of a combination of markers (Rossi et al., 2009a, Kim and Kwon, 2010).
Comparing the reactivity to TTF-1 and napsin A as markers for primary lung ACs, high-sensitivity values were found in the current study. Napsin A was positive in 10 of 12 (83.3%) whereas TTF-1 reactivity was found in only eight (66.7%) AC cases. Moreover, the present study revealed a striking difference in the proportion of positively stained cells for TTF-1 and napsin A in lung AC. Diffuse reactivity (in >50% of tumor cells) was found in two of eight and in seven of 10 cases for TTF-1 and napsin A, respectively.
Regarding the expression of TTF-1 and napsin A in relation to the differentiation grade of AC, our findings of higher expression for napsin A compared with TTF-1 in well-differentiated ACs (100 and 66.6%, respectively) has been documented by previous studies (Ueno et al., 2003; Bishop et al., 2010). Also, decreased expression of both markers in poorly differentiated AC was reported. Bishop et al. (2010) and Zhang et al. (2010) demonstrated that napsin A had more positivity (69 and 33.3%, respectively) than TTF-1 (44 and 28.6%, respectively) among poorly differentiated ACs. Similarly, the present study found napsin A and TTF-1 positivities of 60 and 40%, respectively.
The differential expression of TTF-1 and napsin A in different studies may be caused by the quantity of tumor cells available for staining and a relatively small number of cases studied. This observation still needs to be examined further in a large-scale study (Jagirdar, 2008).
Therefore, we recommend that the use of p63, TTF-1, and napsin A immunostaining can effectively improve the classification of NSCLC into squamous and nonsquamous subtypes, especially in small biopsy specimens. This may eventually be considered for targeted therapy that must exclude SCCs.
There are no conflicts of interest.
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