Radiation-induced malignant meningioma following proton beam therapy for a choroidal melanoma

We report a woman with malignant meningioma diagnosed 9 years after the treatment of a choroidal melanoma with proton beam therapy. The risk of secondary cancers is a well-known adverse late effect of radiation therapy, especially with the use of advanced techniques such as intensity-modulated radiation therapy. However, this risk may be less with the use of proton beam therapy. A 79-year-old woman presented with symptoms of enophthalmos, ptosis and paralysis of the left medial rectus muscle. She had previously been successfully treated for a choroidal melanoma of the left eye with proton beam therapy (total dose: 60 cobalt gray equivalents) following local resection. MRI showed a lesion in the left cavernous sinus with extension into the orbit and a subsequent biopsy revealed a papillary meningioma. The cavernous tumor was treated with photon radiotherapy (total dose: 54Gy) which achieved an initial partial response. However, 8 months later the tumor extensively metastasized to the skull and the spine and the patient died 1 year after the treatment. The incidence of secondary malignancies after proton beam therapy is low but not negligible, therefore, it must be taken into account when planning a treatment as secondary tumors may present with a highly aggressive behaviour.