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Chapter 7: ALK Analysis in Cytology
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Figure 2. Representative findings on ALK FISH testing of on conventional cytologic slides or previously Papanicolaou-stained tissue (compressed z-stacked images showing the projection of all FISH signals in the intact cell nuclei). 2A and 2B: Two ALK-negative cancers with three normal (fused) ALK signals (2A), and with higher numbers of normal ALK signals per tumor cell nucleus (2B). 2C and 2D: Two ALK-positive cancers with one or two break-apart signals (a distance between green and red signals of at least two times the diameter of the signal) (2C) or a single red signal with no corresponding green signal in addition to several normal signals per tumor cell nucleus (2D).
on unstained specimens as well as those processed with Papanicolaou, hematoxylin, or a modified Giemsa stain, and a separate procedure is not usually required, except for when a modified Giemsa stain is used and de-staining with an acid-alcohol technique is recommended before FISH analysis (Betz 2013). Notably, FISH also applies well to immunocytochemically stained specimens if 3-amino-9-ethylcarbazol (AEC) is used as a chromogen; use of 3, 3' diaminobenzidine (DAB) can interfere with the FISH signals because of autofluorescence. A protocol for FISH on stained cytologic specimens has been published (Thunnissen 2012b). There may be concerns about using diagnostic cytologic slides for FISH analysis because of a legal requirement that cytology laboratories archive diagnostic slides for several years and the potential need to review slides related to rare cases even years after diagnosis. These concerns can be addressed by capturing representative images or by scanning the whole slide before analysis. It is also possible to re-stain slides after FISH analysis (Betz 2013).