Which of the following are considered low risk features for neuroblastoma patients?

a. Age less than one year

b. Stage 2A and 2B disease (International Staging Criteria)

c. Stage 4S disease (International Staging Criteria)

d. Neuron specific enolase plasma level less than 100 ng/ml

 Risk status is determined in neuroblastoma patients by a number of characteristics which have been elaborated over the last twenty years.