ALK Protein Expression Correlates with ALK Rearrangement, but Not Increased ALK Copy Number in Lung Adenocarcinomas
Bing Ren, Loralee A McMahon, Qi Yang, Nancy Wang, Paul Rothberg, Zhongren Zhou, Faqian Li, Haodong Xu. University of Rochester Medical Center, Rochester, NY
Background: A small subset of non-small cell lung carcinomas (NSCLCs) harboring anaplastic lymphoma kinase (ALK) gene rearrangement are responsive to ALK inhibitor therapy. A novel, highly sensitive antibody against ALK has been developed for detecting ALK-rearranged lung adenocarcinoma. However, ALK expression in NSCLCs with increased ALK copy numbers is largely unknown. Our study aimed to evaluate the ALK expression in NSCLCs with ALK rearrangement and copy number change.
Design: ALK genetic status was determined by FISH using break apart probes in total 59 cases of NSCLC, including 20 confirmed extrapulmonary metastases, 20 lung biopsies, and 19 lung resection specimens. Fifty four cases were also analyzed for mutations in exons 19 and 21 of the EGFR gene using Sanger sequencing. ALK protein expression was detected by immunostain using a monoclonal antibody (Cell Signaling Technology) in 36 cases (5 ALK-rearranged adenocarcinomas, 19 NSCLCs with increased ALK copy numbers, and 12 normal ALK NSCLCs).
Results: Among 59 total cases, FISH analysis showed 7 adenocarcinomas with ALK gene rearrangement, 19 NSCLCs (16 adenocarcinoma, 2 squamous carcinoma and 1 adenosquamous carcinoma) with increased ALK copy numbers, and 33 NSCLCs (29 adenocarcinoma, 1 adenosquamous carcinoma, and 3 not otherwise specified NSCLCs) with normal ALK. One adenocarcinoma with increased ALK copy number and two adenocarcinomas with normal ALK harbored activating EGFR mutations. Positive ALK protein expression was observed in 80% (4/5) of ALK-rearranged adenocarcinomas, with 3 of them exhibiting moderate to strong staining in more than 90% of the tumor cells and one showing weak staining in 80% of the tumor cells. No ALK protein expression was detected in NSCLCs with increased ALK copy numbers or normal ALK. Immunostain failed to detect one ALK-rearranged adenocarcinoma which had only 6.5% cells with split signals. Five of 20 (25%) extrapulmonary specimens and 2 of 39 (5.1%) pulmonary cases had ALK rearrangement (p<0.05).
Conclusions: Our study indicates that immunohistochemical staining for ALK could be used as a surrogate assay to screen ALK-rearranged adenocarcinoma for targeted therapy. Also our results indicate a possible association of ALK rearrangement with metastatic lung adenocarcinoma. The clinical significance of increased ALK copy number in NSCLC merits further study.
Monday, March 4, 2013 1:00 PM
Poster Session II # 280, Monday Afternoon