Detection and Clinicopathologic Features of ALK Rearranged Lung Adenocarcinoma.
Daphne C Ang, James Matthew Reinersman, Suresh C Jhanwar, William Travis, Marc Ladanyi. Memorial Sloan-Kettering Cancer Center, New York, NY
Background: The EML4-ALK fusion in lung adenocarcinomas (AD) is mutually exclusive with EGFR and KRAS mutations and is associated with striking responses to ALK kinase inhibitors. The optimal detection strategy and morphologic features of this genetic subset of lung AD remain poorly defined. We compared ALK fusion detection by fluorescence in situ hybridization (FISH), immunohistochemistry (IHC), and reverse transcriptase-polymerase chain reaction (RT-PCR), and then used this highly validated set of cases to examine the clinicopathologic features of ALK-rearranged (ALK-R) tumors.
Design: We screened 622 EGFR and KRAS wild type lung AD for ALK rearrangement by dual color split signal FISH assay (Abbott-Vysis; positivity defined as presence of split signals or loss of 5' ALK probe in >5% of tumor cells); 32 ALK-R and 99 ALK-germline (ALK-G) tumors were then tested by IHC [ALK D5F3 monoclonal antibody, Cell Signaling; scored as negative (0-1+) and positive (2-3+)], and RT-PCR (using 6 EML4 forward primers; 1 ALK reverse primer).
Results: Of the 622 cases tested by FISH, 48 (8%) cases were ALK-R and 571 (92%) were ALK-G. As EGFR- and KRAS-germline cases make up about 55% of lung AD in our population, we estimate a 4% overall prevalence of ALK fusion. The most common predominant histology was solid (54%), followed by acinar (17%) and papillary (Pap 8%). Signet ring cells were identified in 7 cases (15%) including solid (n=5), Pap (n=1) and Micropapillary (MP, n=1) subtypes. ALK-R tumors were strongly associated with non-smokers, solid-predominant histology and high stage (IIIB-IV) at presentation. The concordance rate of IHC and RT-PCR assay with FISH were 97% (77/79; k=0.95) and 95% (131/138; k=0.88), respectively. All 99 ALK-G tumors by FISH were negative by IHC and RT-PCR.
Conclusions: Our study suggests that FISH should be combined with IHC as a screening strategy for ALK fusions in routine practice, with confirmation by RT-PCR as needed. IHC can raise diagnostic accuracy in cases with low % of FISH-positive cells (5-15%). All FISH-positive cases in this low range were confirmed by IHC/RT-PCR. ALK-R tumors are associated with poorly differentiated lung AD (solid, MP). However, signet ring cells are identified in only 15% of ALK-R tumors.
|ALK-R (n=48)||ALK-G (n=99)||P value|
|Age (median)||31-84 (58)||35-87 (63)|
|Female||21 (44%)||60 (61%)||0.1029|
|Male||27 (56%)||35 (39%)|
|Non-Smoker||40 (83%)||21 (21%)||<0.0001|
|Smoker||8 (17%)||78 (79%)|
|Stage IA-IIIA||12 (25%)||67 (68%)||<0.0001|
|Stage IV||36 (75%)||32 (32%)|