In a cohort of 55 primary meningiomas, classified atypical according to the 2021 WHO criteria, and that underwent complete surgical resection and no adjuvant radiotherapy, immunostaining for MCM2 or ACADL in ≥ 20% tumor cells was significantly associated with recurrence and with shorter RFS, without any significant difference between tumors showing only ACADL immunostaining (corresponding to MG3) or both ACADL and MCM2 positivity (equating to MG4). The gene discussed is MCM2; the disease is meningioma.