Can ALK Immunohistochemistry Reliably Identify ALK-Translocated Non-Small Cell Lung Cancer?
Juraj Bodo, Lucian R Chirieac, Lisa Durkin, Eric D Hsi. Cleveland Clinic, Cleveland, OH; Brigham and Women's Hospital, Boston, MA
Background: Demonstration of ALK rearrangement in non-small cell lung cancer (NSCLC) tissue is required for guiding targeted therapy with ALK-inhibitors (e.g. crizotinib). Fluorescence in situ hybridization (FISH) is considered the gold standard method for detecting ALK rearrangement. Detection of ALK protein expression by immunohistochemistry (IHC) might be a more rapid and cost effective screening technique for determining which cases to refer ALK translocation testing. We evaluated the correlation between ALK protein expression in NSCLC by IHC and ALK rearrangement by FISH. Moreover, we quantified protein expression levels relative to ALK+ anaplastic large cell lymphoma (ALCL) to further understand differences from ALCL, in which IHC has supplanted FISH as a surrogate for ALK translocation.
Design: A total of 34 NSCLC samples with known ALK FISH status (9 positive, 25 negative) were stained using automated IHC (Leica, Bond-Max) with an ALK specific antibody (clone 5A4). In positive lung cancer samples ALK was quantified using quantum dot (QD) nanocrystal fluorescent detection system. Results were compared with a series of ALK+ ALCLs also analyzed by QD using multispectral image analysis (Nuance, v2.10.0)
Results: All 9 cases were positive for ALK expression by IHC. There were no false positive or negative IHC results. By IHC the majority of tumors cells were positive in ALK rearranged cases, although intensity of staining varied from weak to moderate. Interestingly, the level of ALK expression was significantly variable among these cases too, and by QD analysis we observed a greater than 20-fold difference between the lowest and highest expression levels. Overall, the levels in lung cancer were 20-fold lower, on average, than those found in primary ALCL (P< 0.001, 2-tailed T-test).
Conclusions: IHC with clone 5A4 and polymer detection system performs well in recognizing ALK+ NSCLC. With further validation it should prove useful as either a screening technique or a potential surrogate for FISH testing. Compared to lymphoma, IHC assays for ALK in NSCLC must be highly sensitive since expression levels are much lower in NSCLC. An alternative explanation might be a higher sensitivity of this clone for the EML4-ALK fusion protein.
Tuesday, March 20, 2012 9:30 AM
Poster Session III # 305, Tuesday Morning