Primary mismatch repair-deficient IDH-mutant astrocytoma in child: Unusual entity.

INTRODUCTION

"Primary Mismatch Repair-Deficient IDH-mutant Astrocytoma" (PMMRDIA) is a newly identified high-grade glioma with a poor prognosis. It has not been officially recognized as a distinct entity in the 5th edition of the WHO Classification of Central Nervous System Tumors 2021, making its diagnosis challenging.

CASE PRESENTATION

To highlight this entity, we present the case of a 7-year-old boy with a family history of cerebral tumor among the father's relatives and first-degree parental consanguinity. He experienced increased intracranial hypertension and inguinal café-au-lait macules. Brain imaging revealed a cystic and solid mass with irregular enhancement in the left parietal lobe, indicating a possible Pilocytic astrocytoma. The final diagnosis of PMMRDIA was confirmed through histological, immunohistochemical, and molecular analysis.

CLINICAL DISCUSSION

This tumor is mainly observed in children and is characterized by microsatellite instability (MSI) and high tumor mutational burden (TMB). MSI is known to occur in recurrent IDH-mutant gliomas as a resistance mechanism towards alkylating chemotherapy.

CONCLUSION

In PMMRDIA, MSI can be a good predictive biomarker for responding to immunotherapy, which could improve the outcome of these children.