Purpose: The majority of relapsed neuroblastomas have mitogen-activated protein kinase (MAPK) pathway activating mutations. We previously showed the in vitro and in vivo anti-tumor effects of MAPK/ERK kinase (MEK) inhibitors in MAPK-activated neuroblastoma. We herein assessed the correlation between MAPK activation and the prognosis in neuroblastoma patients using phosphorylated extra-cellular signal-regulated kinase (pERK) immunohistochemistry to establish the protocol for the clinical administration of MEK inhibitors. Methods: Neuroblastoma samples from patients treated in our hospital were immunostained with pERK. The clinical outcomes were retrospectively collected from medical records. The correlation between pERK positivity and the prognosis was analyzed. Results: Regarding pre-chemotherapeutic specimens, there were no differences in the pERK status between tumors with a good and bad prognosis in both the nuclei and cytoplasm. Regarding post-chemotherapeutic specimens, one of eight tumors with a good prognosis and four of six tumors with a poor prognosis showed pERK-positive nuclear staining (p = 0.0909) and five of eight tumors with a good prognosis and four of six tumors with a poor prognosis showed pERK-positive cytoplasmic staining (p > 0.9999). Conclusion: These findings suggested post-chemotherapeutic—not pre-chemotherapeutic—nuclear pERK-positive neuroblastoma tends to be associated with a poor prognosis and may be a potential therapeutic target for MEK inhibitor treatment.
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