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Chapter 8: Reporting of ALK Testing
• Percentage of tumor cells on initial section/block and optionally after cancer-cell enrichment, such as macrodissection, to reflect the tumor cellularity of the sample part used for DNA/RNA isolation • Extent of necrosis, inflammatory cell infiltrates, anthracosis, and tissue artifacts • Test results of additional diagnostic immunohistochemical markers, such as thyroid transcription factor-1 (TTF-1), p63/p40, and mucin stains, if available (Thunnissen 2012a) Overall specimen adequacy • Documented as “adequate for testing” (relative to the findings noted here, as well as for ALK testing) or as “suboptimal” (with notation of the reason or reasons) Other information • Past drug treatment, if available (optional)
Analytic Section
This section should include the basic methodology for each assay used, along with the assay sensitivity and threshold. The information should be sufficient enough for another laboratory to understand what was done, in the event of a discrepancy between laboratories, or if asked to repeat testing. • ALK FISH: probe set (manufacturer, type) and threshold used to define a positive result • ALK IHC: antibody type (source), antibody concentration, incubation time and temperature, and secondary signal enhancement system • ALK RT-PCR: method used, primers, probes and their references, and assay sensitivity
Results Section
This section should report the outcome of the test, including incidental ?ndings and variants of uncertain signi?cance. Inconclusive results should be clearly reported as such. The results should be reported as positive or negative for ALK rearrangement so that oncologists and nonspecialist pathologists can readily understand the results. In addition, specific elements should be reported according to the testing method used. ALK FISH: the number of cells analyzed and the number and percentage of cells displaying positive patterns; if an atypical pattern was seen, it should be noted (for example, “negative for ALK rearrangement, see Interpretation”); if International Systems for Human Cytogenetic Nomenclature (ISCN) is used, it should be accompanied by an easily understandable discrete result ALK IHC: The result should be reported as positive, negative, or indeterminate; when the result is indeterminate, an explanation should be provided (e.g., tumor tissue exhaustion, insufficient number of tumor cells); other optional results are the modified H-score (the percentage of stained nuclei, the intensity of staining, and the staining pattern [cytoplasmic and/or membranous]) and the homogeneity of staining. To ensure the validity of the technique, an external positive control is required for all tests. This positive control can be a cell block with an ALKrearranged cell line or an ALK-positive tumor specimen.