Amplification of c-myc oncogene by chromogenic and fluorescence in situ hybridization in archival breast cancer tissue array samples

Fluorescence in situ hybridization (FISH) is currently considered to be the most specific and sensitive method for detection of oncogene amplification s in human tumor samples. However, FISH requires fluorescence microscopy, w hich is tedious and does not allow histopathologic evaluation of the cells and tissues examined. Here we compared FISH with the newly developed chromo genic in situ hybridization (CISH), which uses peroxidase enzyme for probe detection instead of fluorescent dyes. CISH was found to be highly concorda nt with FISH in a tissue array series of 177 archival breast cancer samples . This was true both when comparing CISH with single-color and two-color FI SH, the latter including the chromosome 8 centromere probe as reference (th e kappa coefficients were 0.67 and 0.76, respectively). Clinicopathologic c orrelations of c-myc amplification as detected by FISH and CISH were genera lly the same. By both methods, c-myc amplification was significantly associ ated with high histologic grade, negative progesterone receptor status, DNA aneuploidy, and high S-phase fraction. c-myc amplification was strongly as sociated with poor distant metastasis-free survival when amplification was detected by CISH (P = 0.0013), but this association was weaker when FISH wa s used (p = 0.16 for two-color FISH and p = 0.065 for single-color FISH). T hese data suggest that CISH is at least as sensitive and specific as FISH i n the detection of oncogene amplification in human tumor samples. The possi bility for concomitant tissue architecture evaluation using an ordinary tra nsmitted light microscope may favor the use of CISH over FISH in oncogene a mplification detection in large tumor series, and tissue arrays and, ultima tely, in routine clinical diagnostics.