Immunocytochemistry (ICC):
In all cases with undifferentiated morphology, a suitable panel was applied for confirmation of neuroblastoma (positivity for neuronal markers like chromogranin, synaptophysin, and PHOX2B) and its differentiation from other small round blue cell tumors (negativity for other markers like CD45, CD99/MIC2, Vimentin, desmin, myogenin). ICC for ALK protein was performed on cell blocks with adequate cellularity. The recommended staining protocol for VENTANA anti-ALK (D5F3 clone) CDx Assay and Rabbit Monoclonal Negative Control Ig with Opti View DAB IHC Detection Kit and Opti View Amplification Kit on a Benchmark XT instrument was followed. Positive control  for immunocytochemistry was taken as section of appendix/colon with ganglion cells. ICC scoring was carried out using H-score wherein the tumor cell percentage positivity (in increments of 10) with 0, 1+, 2+ and 3+ intensity was evaluated. The percent positivity multiplied by the intensity was added up to obtain the final H-score as follows: H score= (0x % positive) + (1+x % positive) + (2+x % positive) + (3+x % positive). A cut-off of 100 was taken for statistical analysis with a score>100 being moderate to high ALK expression.