Clinicopathologic implication of ALK rearrangement in surgically resected lung cancer

Abstract

Background

To characterize the clinicopathologic features of ALK-rearranged lung cancer, and suggest a molecular test protocol for lung adenocarcinoma in the small biopsy specimen.

Methods

In 735 NSCLC surgical specimens, clinicopathologic features, ALK protein over-expression by immunohistochemistry (IHC), and ALK rearrangement by fluorescence in situ hybridization (FISH) as well as EGFR and KRAS mutation studies were analyzed.

Results

Of the 735 NSCLC cases, 28 (3.8%) were ALK FISH-positive. ALK rearrangement, EGFR and KRAS mutation were mutually exclusive. ALK rearrangement was significantly higher in adenocarcinomas (6.8%, p < 0.001), younger age (p < 0.0007), women (7.6%, p < 0.001), and never-smokers (8.9%, p < 0.001) with no gender difference in the adenocarcinoma or never-smoker subgroup. ALK FISH-positivity was not associated with disease recurrence (HR, 0.79; 95% CI, 0.42–1.49) or overall survival (HR, 0.61; 95% CI, 0.24–1.55). However, ALK-rearranged lung cancer tended to show more frequent lymph node metastasis despite its lower T stage. Similar to EGFR-mutated lung cancer, ALK-rearranged lung cancer was enriched in adenocarcinoma, women, and never-smokers. The results of ALK IHC and FISH obtained from tissue microarray (TMA)/biopsy specimens and whole sections after resection were concordant.

Conclusion

ALK rearrangement was not a significant prognostic factor in surgically resectable NSCLC. The clinical profiles of ALK-rearranged lung cancer patients overlapped with those of EGFR-mutated patients. Therefore, we suggest that simultaneous tests for ALK IHC and EGFR mutation (Chung's SNUBH molecular test protocol), which has important implications for the storage and use of small biopsy or cytology samples for genetic analysis.

Introduction

Lung cancer is the leading cause of cancer-related mortality in both men and women [1], and non-small cell lung carcinoma (NSCLC) accounts for ∼85% of lung cancer cases [2]. Although surgical resection is the choice of curative treatment, the majority of the patients with NSCLC are diagnosed at the advanced, unresectable stage. Historically, the pathologic stage has been used to define groups with similar treatment strategies, and is the most important predictor of survival in patients with NSCLC [3], [4].

However, NSCLC is now considered as a heterogeneous disease based both upon molecular features as well as histologic subtypes [5], [6]. In the last 5 years, it has also become evident that adenocarcinomas are characterized by distinct genomic changes that allow the tumors to be further classified into clinically relevant molecular subsets [7], [8], [9]. A representative is a subset of lung cancer patients with EGFR mutations that showed better response rates and prolonged progression free survival when treated with EGFR tyrosine kinase inhibitors (TKIs) than standard platinum-based chemotherapy [10]. Therefore, a selection of the patients based on a biomarker testing has become an essential prerequisite for the appropriate use of targeted therapies in NSCLC.

Recently, Soda et al. have identified the EML4 (echinoderm microtubule-associated protein like 4)-ALK (anaplastic lymphoma kinase) fusion gene in a subset of NSCLCs [11]. ALK-rearranged lung cancer is a unique NSCLC category that is characterized by ALK gene inversion or translocation, and mutually exclusive from other well-known oncogenic mutations involving EGFR or KRAS. Despite the relatively low frequency of the EML4-ALK fusion [12], [13], [14], [15], ALK-rearranged lung cancer has been considered as a unique subgroup with a striking response to treatment with a small-molecule inhibitor of ALK [16].

For the understanding of this patient group, it is important to characterize the clinicopathologic features and prognostic implications of ALK rearrangement in NSCLC, which has not yet been clarified. Furthermore, the efficient separation of the patients with ALK rearrangement from those with EGFR mutation by molecular tests using small biopsy materials is an emerging issue with great clinical interest. In many clinical situations with lung cancer patients including inoperable and/or unresectable condition, the limitation of the amount of biopsy material raised the question of which molecular test should be prioritized for the appropriate targeted therapy. The clinicopathologic characterization of ALK-rearranged lung cancer in the large-scale cohort may provide a possible answer to the clinically important question.

In this study, we aimed to contribute to (1) clinicopathologic characterization of the ALK-rearranged lung cancer in the surgically resectable patients, and (2) suggestion of a “tissue-saving” algorithm for molecular tests of adenocarcinoma with small lung biopsy samples. To make the clinical features clear, we constructed and analyzed retrospective cohort of the patients with primary lung cancer from two institutions in Korea by excluding the patients with stage 4 disease, previous history of cancer, presurgical chemotherapy or radiotherapy. For the clinicopathologic characterization including prognosis with this rare subgroup, it was inevitable to constitute a large-scale cohort by including parts of the previously reported NSCLC patient set where the correlation between immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) was analyzed [12], [13].