IASLC Sept 2013 | Page 30

Chapter 4
Immunohistochemistry (IHC)
By Erik Thunnissen, Sylvie Lantuéjoul, Jin-Haeng Chung, Keith Kerr, Fred R. Hirsch, Ming Sound Tsao, and Yasushi Yatabe

ALK IHC as a Screening Tool
Molecularly targeted therapy is critically dependent on a validated test to detect the corresponding molecular alteration, especially when the molecular alteration is present in a small subgroup of patients. ALK IHC holds promise as a rapid and relatively inexpensive screening method that uses bright-field examination, which is preferred by most pathologists primarily because it allows the evaluation of tissue architecture and tumor cell histology. Potentially, IHC can be interpreted with fewer malignant cells than needed for FISH. IHC can be performed successfully on a variety of different tumor specimens; FFPE tissue blocks, fluid, and FNA cytology cell blocks or smears can be tested as long as at least a few clusters of viable tumor cells are present in the specimen. In addition, with a disease of low prevalence such as ALK-rearranged NSCLC, there is a growing need for an economic screening method (Soda 2007, Koivunen 2008, Perner 2008, Takeuchi 2008, Palmer 2009).

The Challenge of ALK IHC
It is important to standardize the ALK IHC assay as a screening method and to establish the evaluation criteria. The tumor cells in ALK-positive lung cancer usually express the protein product of the ALK chimeric genes (Figures 1 and 2). The fusion protein of the intracellular tyrosine kinase domain of ALK with various (N-terminal) truncated portions of the partner gene is responsible for constitutively increased ALK kinase activity (Morris 1994, Allouche 2007). However, the ALK fusion protein in NSCLC may be more difficult

A

B

C

D

Figure 1. An adenocarcinoma that is strongly ALK positive. A and B: H & E-stained slides, with an overview (A) and at a magnification of x10 (B). The inset in B is at a magnification of x40. No signet ring cells are seen. C and D: ALK IHC with the 5A4 antibody shows intense cytoplasmic staining of ALK gene product (magnification, C: x20, D: x40).