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- Materials and Methods
- Supporting Information
Adenosquamous carcinoma of the lung (Ad-Sq) is an uncommon subtype with poor prognosis. We analyzed the clinicopathological characteristics of Ad-Sq, focusing the correlation between Epidermal Growth Factor Receptor (EGFR) mutation and clinicopathological factors. A total of 67 cases were selected from September 1992 to May 2011. EGFR mutational analysis (n = 59) was performed by direct sequence. We also performed immunohistochemical staining for EGFR mutated cases using the two mutation-specific antibodies for deletion and L858R. Postoperative 3-year survival rate of Ad-Sq was 58.7%, statistically worse in comparison with adenocarcinoma (58.7% vs. 78.1%, P = 0.038). Twenty-four percent (14/59) were positive for EGFR mutations. Patients who had never been smokers and who were lymphatic permeation positive were seen more frequently in the mutation positive group (P = 0.035, 0.027, respectively). Moreover, the EGFR mutated group tended to have a more positive prognosis than negative. Focusing on the pathological features, the lepidic growth pattern was more frequently seen in the positive group (P = 0.018). Immunoreactivity for the DEL-specific and L858-specific antibody were observed in both adenocarcinoma and squamous cell carcinoma components. Our study demonstrated that EGFR mutated Ad-Sq had similar clinicopathological features as EGFR mutated adenocarcinoma.
Adenosquamous carcinoma of the lung (Ad-Sq), which is defined as a carcinoma containing components of both squamous cell carcinoma (Sq) and adenocarcinoma (Ad) and with each component comprising at least 10% of the tumor, is an uncommon subtype, accounting for 0.4 to 4% of all non-small cell lung cancer cases.
Because of its rarity, the clinicopathological aspects of Ad-Sq have not received much attention, and the pathogenesis of Ad-Sq remains unknown. In general, the prognosis of Ad-Sq was reportedly worse than that of Ad and Sq.[2, 3]
Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib and erlotinib, are therapeutic options widely used for the treatment of Ad patients. The responders to EGFR-TKI have somatic mutations in the EGFR tyrosine kinase domain, including deletions in exon19 and a point mutation at codon 858 in exon21 (L858R). For these patients, EGFR-TKI has a high response rate of approximately 70% and results in better prognosis.[4-7]
However, the usefulness of EGFR-TKI treatment is limited to Ad, and few studies have analyzed the effectiveness of EGFR-TKI for Ad-Sq. Until recently, EGFR mutation in Ad-Sq has been mentioned in only a few reports. Sasaki et al. reported that 4 (15%) of 26 Ad-Sq patients were positive for EGFR mutations, which is a lower frequency than that for Ad. On the other hand, Kang et al. reported that 11 (44%) of 25 Ad-Sq patients were positive for EGFR mutations among a Korean population.
In the present study, we selected 67 Ad-Sq cases and investigated the clinicopathological characteristics of Ad-Sq. Focusing on the EGFR mutation in Ad-Sq, we analyzed 59 Ad-Sq cases with special reference to the correlation between mutation status and clinicopathological factors. Additionally, we performed immunohistochemical staining for the EGFR-mutated cases using two mutation-specific antibodies for a deletion and L858R to detect the distribution of mutated cells in each component.
- Top of page
- Materials and Methods
- Supporting Information
In this study, we analyzed the clinicopathological characteristics of Ad-Sq, focusing on the correlation between EGFR mutations and clinicopathological factors. This is the first study to demonstrate that EGFR-mutated Ad-Sq had clinicopathological features, similar to those of EGFR-mutated adenocarcinoma, specifically to never having been a smoker, better prognosis, and pathologically lepidic growth pattern. It was suggested that Ad-Sq of the lung could be subclassified into distinct subtypes with different pathogenetic mechanisms according to the EGFR mutation status.
Until recently, a few studies have analyzed EGFR mutations in Ad-Sq.[8, 9, 14-17] However, we analyzed 67 cases of Ad-Sq, the largest number of cases among similar studies published to date. Moreover, we performed a clinicopathological analysis using not only a molecular method, but also immunohistochemistry with two mutation-specific antibodies.
In our study, the frequency of the EGFR mutation in Ad-Sq was 24% (14/59). In the previous studies, Sasaki et al. reported that 4 of 26 (15%) Ad-Sq were positive for an EGFR mutation, and Toyooka et al. reported that 3 of 11 (27%) cases were positive, similar to the results of the present study.[8, 15] On the other hand, a discrepancy was observed with regard to the frequency of EGFR mutation when compared with results obtained in neighboring countries. Kang et al. reported that 44% (11/25) of Ad-Sq were positive for an EGFR mutation in a Korean population, and Xiao et al. reported a frequency of approximately 38% (21/55) in a Chinese population.[9, 17] This discrepancy might be attributable to differences in the detection methods used for the mutational analysis; alternatively, genetic differences between Japanese populations and others may also affect the frequency of mutation.
The sensitivity of the DEL-specific antibody used in our study was inferior to that of the L858R-specific antibody, as previously reported.[18-22] Kozu et al. reported that the sensitivities of DEL-specific and L858R-specific antibodies were 42.2% and 75.6%, respectively. Immunohistochemical staining revealed that the EGFR mutation occurred not only in the Ad component, but also in the Sq component. Staining intensity in both components was similar, as shown in Fig. 4 and Table 4. Several studies using microdissection analyses have demonstrated identical EGFR mutations in both components, but few immunohistochemical analyses have been performed. Recently, Miyamae et al. demonstrated that identical EGFR mutations were observed in the Ad and Sq components using a DEL-specific antibody, suggesting that Ad-Sq to be generated from monoclonal origin. Rekhtman et al. described that squamous cell carcinoma with EGFR mutation had a component of adenocarcinoma using immunohistochemistry. These findings may suggest that squamous cell carcinoma componemt was originated from adenocarcinoma somponent in Ad-Sq. In contrast, Kanazawa et al. described the monoclonal transition from squamous cell carcinoma to adenocarcinoma. So, it is difficult at this time to conclude the origin of Ad-Sq.
Interestingly, a lepidic growth pattern was more frequent in the EGFR-mutated group than in the negative group. Blons et al. reported that EGFR mutations in Ad were more prevalent among cases with a lepidic growth pattern. In this study, we detected the same correlation between the EGFR mutation status and the lepidic growth pattern in Ad-Sq as well as Ad. Sasaki et al. reported that the EGFR mutational status of Ad-Sq was significantly correlated with the smoking history and gender. Kang et al. also reported that EGFR mutations in Ad-Sq were more frequent among people who had never been smokers and women. The current study revealed a similar correlation with smoking, but we did not find a significant correlation with sex.
A Kaplan–Meier survival curve showed that the survival of the EGFR-mutated cases was better when compared with the negative cases, even though a statistically significant difference was absent. Although a similar tendency was observed in Ad cases,[27, 28] no previous studies have compared the survival of EGFR-positive Ad-Sq cases with those of EGFR-negative cases. In the future, large-scale, multi-institutional studies will be needed to verify the results.
In this study, we found several common features between EGFR-mutated Ad-Sq cases and those with Ad. Therefore, we speculated that a subtype with clinicopathological features resembling those of Ad existed among the Ad-Sq tumors with an EGFR mutation. Based on our analysis, Ad-Sq developing in a patient who had never been a smoker and pathologically exhibiting a lepidic growth pattern in the Ad component was likely to be positive for an EGFR mutation. EGFR-TKIs, such as gefitinib and erlotinib, may be effective therapeutic options for patients with EGFR-mutated Ad-Sq as well as those with EGFR-mutated Ad. Mitsudomi et al. have reported excellent clinical response to gefitinib in a patient with EGFR mutated Ad-Sq. Shukuya et al. reported that efficacy of EGFR-TKIs for non-adenocarcinoma with EGFR mutation was different from that of pure adenocarcinoma. So, we consider that further large-scale clinical trials of EGFR-TKI for adenosquamous carcinoma patients are needed, as is validation of an optimal therapeutic strategy.
As shown in Fig. 4, some cancer cells showed positive reaction for mutation specific antibodies. Although biological significance of this nuclear staining pattern is not clarified, further examination will be required.
In conclusion, we demonstrated that EGFR-mutated Ad-Sq exhibited characteristics similar to those of EGFR-mutated Ad in that they were more likely to occur in patients who had never been smokers and more likely to exhibit a lepidic growth component pathologically. Moreover, patients with EGFR-mutated Ad-Sq tend to have a better outcome, compared with the EGFR-mutation-negative group. So we found the correlation between EGFR mutation and the prognosis of adenosquamous carcinoma of lungs, similar to that of adenocarcinomas. In particular, Ad-Sq cases that carry an EGFR mutation might respond to EGFR-TKI therapy.