MYCN amplification by Fluorescence in situ hybridization (FISH):
FISH was performed either on smears (liquid-based preparation / destained MGG stained smear)  or on cell block section using Vysis LSI N-MYC (2p24) spectrum green/ CEP 2 spectrum orange FISH probe (Abbott Laboratories, USA) and visualized by Olympus BX-51 FISH imaging system. A minimum of 100 nuclei were evaluated in all cases and > 10 MYCN  signals were taken as positive for amplification. Ploidy was determined by counting the number of signals with the CEP probe.