A nurse is caring for a child who has retinoblastoma that has potentially metastasized to the brain. Which of the following diagnostic tests should the nurse anticipate for determining if metastasis of the brain has occurred?

A. Lumbar puncture: A lumbar puncture allows analysis of cerebrospinal fluid (CSF) for the presence of malignant cells, which is essential in detecting central nervous system metastasis from retinoblastoma. This test provides direct evidence of tumor spread to the brain or meninges and helps guide treatment planning. B. Genetic testing: Genetic testing identifies mutations in the RB1 gene, which predispose children to retinoblastoma and assess heritable risk. While important for family counseling and early detection, it does not indicate whether metastasis to the brain has occurred. C. Complete blood cell (CBC) count: A CBC evaluates overall hematologic status and may detect anemia or infection, but it cannot detect CNS metastasis. It is supportive care information rather than a diagnostic tool for brain involvement. D. Bone biopsy: Bone biopsy is used to confirm metastasis to skeletal structures. Retinoblastoma metastasizing to bone requires direct tissue sampling, but this test does not assess brain involvement.