A possible explanation for the discrepancy between the study conducted on neuroblastoma cells on the one hand and our work and the recent study by Cardani and colleagues on the other hand is that neuroblastoma cell lines express nuclear progesterone receptors, which has not been demonstrated in RTN PHOX2B cells even though hypercapnia-induced RTN c-Fos expression is higher in females than males (53). This evidence concerns the gene FOS and neuroblastoma.