Histologic subtyping plays an important role in deciding the course of treatment for patients diagnosed with lung cancer.1 Previous studies have shown that patients respond differently to chemotherapy and targeted therapy depending on the histologic subtypes of their lung cancer.2,3 For instance, patients with stage 4 nonsquamous non-small cell lung cancer (NSCLC) have improved survival and less toxicity when treated with pemetrexed combined with a platinum agent compared with other chemotherapy agents.3,4 Thus, histologic subtyping of NSCLC is now the standard of care for the treatment of lung cancer.5–7 The International Association for the Study of Lung Cancer, American Thoracic Society, and European Respiratory Society recommends that for small biopsy/cytology samples, NSCLCs should be classified into their respective histologic subtypes according to morphologic patterns. When a clear morphologic pattern is not present, immunohistochemical (IHC) staining is suggested to assist with the subtyping.8
In addition to histologic subtyping, treatment of metastatic lung cancer is also guided by the detection of genetic alterations. In patients with metastatic NSCLC who harbor an epidermal growth factor receptor (EGFR) gene mutation, targeted therapy with EGFR tyrosine kinase inhibitors (erlotinib or gefitinib) are recommended as first-line treatment because of greater response rates and longer progression-free survival compared with standard chemotherapeutic regimens.9–12
In addition, in patients with echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) rearrangements, treatment with the tyrosine kinase inhibitor crizotinib leads to a high response rate and improved survival.13,14
For these reasons, the ability to obtain tissue adequate for histologic subtyping and molecular analyses is a key component of the evaluation of the lung cancer patient. Electromagnetic navigation is a guidance technology developed to assist with the localization of peripheral lung lesions during bronchoscopy.15,16 Previous studies have reported the diagnostic yield of electromagnetic navigation bronchoscopy (ENB) to be 63% to 74% for peripheral lung lesions.15–18 The pneumothorax rate for ENB has been reported to be between 1.2% and 6%, significantly lower than the pooled 15% rate for transthoracic needle aspiration (TTNA).16,19–21 Here, we aim to assess the accuracy and adequacy of diagnostic samples obtained by ENB for histologic subtyping and molecular characterization of lung cancer.
PATIENTS AND METHODS
We conducted a retrospective analysis of consecutive patients who, between August 2008 and December 2011, underwent outpatient ENB at the Cleveland Clinic Main Campus that resulted in the diagnosis of lung cancer. The study was approved by the Cleveland Clinic Institutional Review Board.
Study data including patient and lung lesion characteristics were collected and managed using REDCap electronic data capture tools hosted at Cleveland Clinic.22 Tumor size, shape, and location were extracted from radiology reports, and when absent, determined by reviewing original computed tomography images. Clinical staging according to the 7th edition of the TNM staging system was recorded, and when not documented, determined by reviewing available imaging reports.23
Cytopathology reports were reviewed for histologic subtyping of lung cancer, and bronchoscopy reports for the diagnostic sampling methods.24 Histologic subtyping was documented as “adenocarcinoma,” “NSCLC, favor adenocarcinoma,” “squamous cell carcinoma,” “NSCLC, favor squamous cell,” “non–small cell carcinoma, not otherwise specified (NOS),” and “small cell carcinoma.” In cases in which the subtype was not determined by morphology alone, IHC stains for TTF-1, p63, and cytokeratin 5/6 were documented when performed. Histologic subtyping of samples obtained by ENB and surgical resection were recorded separately and compared for concordance.
The adequacy of samples for EGFR mutation (real-time-PCR) and EML4-ALK rearrangement (fluorescence in situ hybridization) analyses was determined by the presence of a result or statement that the sample was inadequate in the test report. EGFR testing was carried out at an outside facility (Clarient, Aliso Vieja, CA).
Descriptive statistics for all continuous variables were summarized as means, median, and ranges. Statistical analyses were performed using the commercially available software SPSS, version 17 (SPSS Inc., Chicago, IL).
Sixty-five patients with lung cancer diagnosed by ENB were identified. Their mean age was 71 years (44 to 89 y). Thirty-four patients (52.3%) were females. Twenty-one patients (32.3%) were current smokers, and 41 (63.1%) were former smokers. The median long-axis diameter of the nodules/masses sampled was 24 mm (12 to 57 mm). Fifty-nine (90.8%) were either irregular, lobular, or spiculated. Thirty-seven (56.9%) had clinical stage I or II lung cancer at the time of bronchoscopy (Table 1).
Methods of tissue sampling performed during ENB included brushing, transbronchial biopsy (TBBx) (SuperTrax biopsy forceps, tip diameter 1.7 mm, length 110 cm), 21-G SuperTrax needle aspiration, 22-G Wang needle aspiration, and bronchoalveolar washing. In cases in which only 1 sampling method was diagnostic, TBBx was the most common method (n=8) (Table 2).
A histologic subtype was identified in all 65 cases (100%). Three cases (4.6%) were diagnosed as small cell carcinoma and 62 cases (95%) as NSCLC, of which 51 (78.5%) could be subclassified by morphology only—35 (81.4%) as adenocarcinomas and 16 (84.2%) as squamous cell carcinomas (Table 3). Twenty-two IHC stains were used in 11 (21.5%) cases, of which 8 (18.6%) were NSCLC, favored adenocarcinomas and 3 (15.8%) were NSCLC, favored squamous cell carcinomas. All 22 samples (100%) were adequate for IHC analysis (Table 4). Histologic subtype was concordant between sampling methods when <1 sampling method yielded a diagnosis. For the entire cohort, IHC staining was performed on samples obtained by TBBx (n=12), 21-G SuperTrax needle aspiration (n=1), and 22-G Wang needle aspiration (n=2).
Of the 43 cases of adenocarcinoma classified by ENB, 15 were sent for EGFR mutation analysis. Fourteen (93.3%) were considered adequate for analysis. Two cases were sent for EML4-ALK gene translocation testing, both of which were adequate (Table 4). EGFR mutation testing and EML4-ALK analyses were performed on TBBx samples in all cases except for one in which EGFR mutation analysis was performed on a 22-G Wang needle aspiration sample. The 1 sample inadequate for EGFR mutation analysis was sent from a TBBx sample.
Of the 37 patients with stage I or II lung cancer, 21 were deemed poor surgical candidates because of comorbidities and did not undergo surgical resection of the primary tumor. Sixteen patients underwent surgical resection. Of the 14 cases of ENB classified adenocarcinoma that underwent surgical resection, 13 were confirmed as adenocarcinoma (92.9% concordance). One ENB classified as “NSCLC, favor adenocarcinoma” was found to be a large cell carcinoma after resection and IHC stains performed on the surgical sample. Of the 2 cases of ENB-classified squamous cell carcinomas that underwent surgical resection, one was found to be an adenosquamous carcinoma after resection. In total, there was an 87.5% concordance rate between histologic subtypes obtained by ENB compared with those obtained by surgical resection (Table 3). In the 2 cases that were misclassified by ENB, IHC staining was not performed on the ENB-obtained tissue samples. IHC staining was performed on the surgical specimen for the adenosquamous carcinoma. It was reported as predominantly squamous cell carcinoma based on morphology. In the 1 ENB subtyped adenocarcinoma that was a large cell carcinoma on surgical resection, brushings alone were used to obtain tissue for diagnosis. Tissue from the adenosquamous carcinoma that was subtyped as squamous cell carcinoma on ENB was obtained by brushing, 21-G SuperTrax needle aspiration, and TBBx.
In this study, we sought to determine the adequacy of tissue samples obtained by ENB for histologic subtyping, EGFR mutation, and EML4-ALK translocation analyses. In 65 cases of lung cancer diagnosed by ENB, the samples obtained were adequate for histologic subtyping of lung cancer in all cases. In addition, the histologic subtyping was accurate, with an 87.5% (14/16) concordance rate with surgical specimens. In samples where morphology alone was not able to provide the subtype of lung cancer, IHC staining was able to differentiate between the subtypes. All tissue samples submitted for IHC staining were adequate for the necessary analyses. In addition, 94.1% (16/17) of the samples tested were adequate for EGFR mutation or EML4-ALK translocation analyses.
Previous reports have indicated small biopsy/cytology samples obtained by TTNA, and endobronchial ultrasound-guided transbronchial needle aspiration are adequate for histologic and molecular characterization of lung cancer.25–29 To the best of our knowledge, 2 previous reports have described the adequacy of samples obtained by standard bronchoscopy for IHC staining to subtype lung cancer. In both the studies, specimens were obtained either by bronchial washing or brushing.30,31 ENB is an alternative to TTNA in the evaluation of peripheral, smaller lung lesions, and has been previously described to be effective and safe.15–18 This is the first report describing the effectiveness of ENB in obtaining tissue adequate for histologic subtyping, EGFR mutation, and EML4-ALK translocation analysis. The histologic subtypes of lung cancer from tissues obtained by ENB were accurate when compared with those obtained by surgical resection. The squamous cell carcinoma classified by ENB underwent IHC staining on the surgical sample to confirm the adenocarcinoma component. This suggests that small samples obtained by various bronchoscopic techniques, including ENB, may be inadequate for subtyping mixed tumors because of selective sampling of the tumor. Tissue samples obtained by ENB are not expected to be different from those obtained by traditional bronchoscopy in the evaluation of peripheral lesions, as the methods of sampling tend to be the same.
Histologic subtyping and molecular characterization of late-stage lung cancer is currently required to provide standard of care treatment. Standard chemotherapy regimens are now based on histology, and histology guides the need for EGFR mutation analysis and EML4-ALK testing.1,8 Agents targeting pathways affected by EGFR activating mutations and the EML4-ALK translocation are considered standard of care therapies when alterations are confirmed. A full 45% of patients in our series had stage III or IV disease at the time of the diagnostic ENB.
Many patients with early-stage lung cancer are not well enough to tolerate resection and instead are treated with ablative therapies. Early recurrence after curative intent treatment may occur in locations that are difficult to biopsy. At times, ENB may be the easiest and safest means of obtaining tissue in this group. Although chemotherapy drugs may have limited role in those with early-stage lung cancer treatable with radiation therapy, mutational analysis clearly has value in those with recurrent, metastatic disease.
The importance of histologic subtyping and molecular characterization of early-stage lung cancer is likely to grow over time. Advances in molecular biomarker development may lead to an improved understanding of the need for adjuvant chemotherapy or chemoprevention. In addition, biomarkers capable of prognosticating outcomes and predicting responses to therapy are under development. The results obtained in this study suggest that ENB-obtained samples will be adequate for both histologic subtyping and molecular characterization as future tests are developed.
Our study is limited by its retrospective nature. Not all samples obtained by ENB were sent for IHC staining, analysis of EGFR mutations and EML4-ALK translocations, and the outcomes of interest were on the basis of the review of cytopathology reports. We were not able to assess the concordance of molecular analyses with those performed on surgical specimens. The increased use of endobronchial ultrasound-guided transbronchial needle aspiration for advanced stage disease with mediastinal adenopathy was not reviewed in this study as we set out only to understand the value in peripheral lung sampling.
We conclude that ENB is effective at obtaining tissue samples adequate for histologic subtyping of lung cancer, as well as EGFR mutation and EML4-ALK translocation analysis.
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Keywords:© 2013 Lippincott Williams & Wilkins, Inc.
electromagnetic navigation bronchoscopy; lung cancer; histology; immunohistochemistry; epidermal growth factor receptor (EGFR) mutation; echinoderm microtubule-associated protein-like 4-anaplastic lymphoma kinase (EML4-ALK) translocation