Histological comparison between preoperative and surgical specimens of non-small cell lung cancer for distinguishing between "squamous" and "non-squamous" cell carcinoma

Lung cancer is the leading cause of cancer and mortality from cancer worldwide[1], with 5-year survival rates of <15% across all stages of the disease[2]. Historically, lung cancer is divided into two morphologic types: small cell lung cancer and non-small-cell lung cancer (NSCLC), with NSCLC accounting for approximately 80% to 85% of all histological types of NSCLC[3].

The International Association for the Study of Lung Cancer, the American Thoracic Society, and the European Respiratory Society recently proposed the classification of NSCLC based on examination of small biopsy and/or cytology specimens into six main subtypes: adenocarcinoma (ADC), squamous cell carcinoma (SQC), NSCLC not otherwise specified (NSCLC-NOS), NSCLC with neuroendocrine morphology, NSCLC with squamous and adenocarcinoma patterns, and poorly differentiated NSCLC with spindle and/or giant cell carcinoma[4]. NSCLCs are frequently heterogeneous and approximately 70% of NSCLCs are diagnosed and staged by examination of small biopsy or cytology specimens rather than by examination of surgically resected specimens[5]; thus, in most patients, the diagnosis is based on examination of preoperative specimens alone. Until now, histological subtyping of NSCLC was not considered to be clinically or therapeutically important, because of the lack of existence of differential treatment options for the various subtypes of NSCLC. However, there is now clear evidence to suggest that the classification of NSCLC into pathologic subtypes is important for the selection of appropriate systemic therapy, from both the point of view of treatment efficacy and prevention of toxicity[6, 7]. For example, large phase III clinical trials have demonstrated that ADC is a strong predictive factor for improved outcome following treatment with the combination of pemetrexed with cisplatin compared with SQC[8]. In addition, the presence of common activating mutations in the tyrosine kinase domain of the epidermal growth factor receptor (EGFR) gene (exon 19 deletion and exon 21 L858R mutation) confers strong sensitivity to gefitinib and erlotinib, which are selective tyrosine kinase inhibitors of EGFR[9, 10]. These EGFR mutations are more commonly encountered in ADCs[11]. Furthermore, the use of vascular endothelial growth factor (VEGF) inhibitors (eg, bevacizumab) has been demonstrated to be associated with an increased risk of fatal pulmonary hemorrhage in patients with SQC[12]. The ALK tyrosine inhibitor crizotinib was demonstrated to show marked antitumor activity in NSCLC patients with EML4-ALK translocation, observed in approximately 3 to 4% of patients with ADC[13]. Thus, a molecular testing guideline has been proposed[14].

If pathological findings are missed, especially when differentiating between "squamous" and "non-squamous" histology, determination of the appropriate treatment is difficult. The aim of this study was to compare the preoperative classification of NSCLC based on biopsy specimens with the postoperative classification made on the basis of examination of resected specimens, and to examine how often accuracy about each histological subtypes of NSCLC.

We assessed the accuracy of diagnosis of the histological type of lung cancer between preoperative and surgical specimens. The reported accuracy for bronchoscopic biopsy as compared to histopathology of resected or autopsy specimens for differentiating among histological subtypes of lung cancer is in the range of 62% to 97.5%[15‐19]. In our study, the concordance rates for diagnosis of the NSCLC subtypes between preoperative biopsies and histopathology of surgical specimens was 66.8% (127/190), which seemed to be slightly low as compared to previous reports; however, many studies excluded tumors that were confirmed as not being malignant: in our study, 50 (26.3%) of 190 patients were diagnosed as not having malignant lesions before excision. After patients without malignancies as determined in preoperative specimens were excluded, the concordance rate was 90.7% (127/140). We found a better accuracy for the diagnosis of SQC than for that of ADC (89.3% vs. 80.4%, p = 0.012), which was also in agreement with previous studies[13, 20]. On the other hand, the sensitivity for ADC was slightly better than that for SQC (75.7% vs. 65.6%, p = 0.138), indicating that ADC seems to have little oversight by preoperative specimens.

IHC studies are usually required if obvious morphological features of squamous or glandular differentiation are not identified. Similar to the findings of this study, prior studies found that ~75% of bronchial NSCLC samples may be subtyped using morphology alone, and 93% of all NSCLC cases may be subtyped when combined immunostaining[21]. Other studies also demonstrated that only a low population (6%) of cases remained without a probable subtype after morphologic examination and IHC[22]. The low not-typed rate in these studies suggests that we should perform IHC as a routine utilization for subtyping of difficult cases.

Several factors affect the diagnostic accuracy. The frequency of diagnostic errors induced by some of these factors, including the biopsy size and degree of differentiation has been described[20]. In our study, the tumor size was correlated with the sensitivity and concordance rate: the larger the diameter, the greater the sensitivity and cell type agreement.

Until date, therapeutic decisions are heavily dependent on the histological subtype of lung cancer (SQC vs. non-SQC) and its molecular characteristics (e.g., EGFR mutation and ALK rearrangement states). Furthermore, many previous studies showed the expression and functions of proteins and genes in lung cancer, and it may be significantly related to tumor progression and metastasis[23‐26].

Both EGFR mutation and ALK rearrangements are almost exclusively seen in ADC. According to multiple large phase III crinical trials[11, 27‐29], the new classification recommends that all patients with advanced lung ADC be tested for EGFR mutation, as EGFR tyrosine kinase inhibitors can be used as first-line chemotherapy for patients with EGFR mutations. Crizotinib has been approved by the US Food and Drug Administration (FDA) for advanced ADC with ALK rearrangements[30]. Therefore, testing for EGFR mutations and ALK rearrangements in patients with advanced ADC is no longer only a research tool, and should be performed in clinical practice. On the other hand, several molecular targets such as FGFR1 amplification and DDR2 mutation have been discovered in SQC[31, 32]. Target therapies that might be beneficial in this selected subpopulation have never been reported. These results indicate that misdiagnosis of ADC as SQC in preoperative specimens should be avoided so as to prevent the loss of opportunity to select beneficial molecular-targeted therapy for these patients in clinical practice. Although such a result was not seen, there were three (1.3%) misclassifications between ADC and SQC in the preoperative specimens, and in all, SQC was diagnosed as ADC. Fortunately, there was only a lone patient who might have lost the opportunity to receive EGFR-TKI therapy by missed diagnosis (0.44%, shown as case report).

Our retrospective study had some limitations. First, only half of the patients who underwent surgery received preoperative diagnosis by TBB or CTNB. Second, there may be variability between intra- and inter- pathologist in lung cancer diagnosis. Because a smaller amount of tissue is obtained, the diagnostic assessment might be more difficult and more inconsistencie in the diagnosis of pathologists might occur. In such cases, multidisciplinary approach and expert consultation are recommended[33].

In conclusion, our study suggested that the concordance rate for the diagnosis of NSCLC subtypes, especially "squamous" or "non-squamous" histology, between preoperative and surgical specimens was satisfactory as compared with other reports. Pretreatment diagnosis of lung cancer using small samples is reasonable for selection of the optimal treatment. However, our case report presented above serves to emphasize the need to be aware that diagnosis based on preoperative small samples might be different from that made from surgical specimens, so as to not lose the opportunity for effective treatment.

Written informed consent was obtained from the patient for the publication of this report and any accompanying images.