Continued research in PDT will determine whether the advances shown will mitigate morbidity and mortality, but certainly the potential for this modality to revolutionize the treatment of brain tumors remains. The various uses for PDT in clinical practice should be pursued.

Development of the central nervous system requires proliferation of neuronal and glial cell precursors followed by their subsequent differentiation in a highly coordinated manner. The timing of neuronal cell cycle exit and differentiation is likely to be regulated in part by inhibitors of cyclin-dependent kinases. Overlapping and sustained patterns of expression of two cyclin-dependent kinases, p19 Ink4d and p27 Kip1 , in postmitotic brain cells suggested that these proteins may be important in actively repressing neuronal proliferation. Animals derived from crosses of Ink4d-null with Kip1-null mice exhibited bradykinesia, proprioceptive abnormalities, and seizures, and died at about 18 days after birth. Metabolic labeling of live animals with bromodeoxyuridine at postnatal days 14 and 18, combined with immunolabeling of neuronal markers, showed that subpopulations of central nervous system neurons were proliferating in all parts of the brain, including normally dormant cells of the hippocampus, cortex, hypothalamus, pons, and brainstem. These cells also expressed phosphorylated histone H3, a marker for late G2 and M-phase progression, indicating that neurons were dividing after they had migrated to their final positions in the brain. Increased proliferation was balanced by cell death, resulting in no gross changes in the cytoarchitecture of the brains of these mice. Therefore, p19 Ink4d and p27 Kip1 cooperate to maintain differentiated neurons in a quiescent state that is potentially reversible.Ink4 proteins ͉ Cip͞Kip proteins ͉ p19 Ink4d ͉ p27 Kip1 ͉ neuronal development

A 17-year-old African American female with human immunodeficiency virus infection presented with an unresectable intracranial neoplasm with mass effect upon the brainstem. Stereotactic biopsy revealed an Epstein-Barr virus (EBV)-associated leiomyosarcoma. Radiation therapy and gemcitabine were used to shrink the mass with the aim to make it surgically resectable. Prolonged neutropenia and recurrent skin infections led to the discontinuation of gemcitabine. The mass stabilized after radiation therapy and has decreased in size in 15 months of follow-up. EBV has been demonstrated in most smooth muscle tumors associated with acquired immunodeficiency syndrome and other immunocompromised states. This is the first documented case of an EBV-positive intracranial leiomyosarcoma in a pediatric human immunodeficiency virus patient.

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