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Once in a lifetime.

Cancer of childhood is relatively rare, with an incidence of approximately 80/100,000. Due to the widespread participation in clinical trials through large cooperative groups, great advances have been made in our understanding and treatment of childhood cancer. However, there remain types of cancer so rare or so rarely seen in children that clinical trials are not feasible, even within national cooperative clinical trial groups. So what does the pediatric oncologist do when faced with those ‘‘once in a lifetime’’ cancers? Case reports of unsuccessful outcomes are rarely reported or published, therefore the clinician is left with at best a few anecdotal reports in the literature and his or her best clinical judgment to guide decisions on therapy. In this issue, Shiozawa et al describe a case of primary central nervous system lymphoma (PCNSL) in a previously healthy 9-year-old. PCNSL certainly fits the description of a ‘‘once in a lifetime’’ or rare cancer observed in children. PCNSL accounts for 1% to 4% of all CNS tumors and 2% of all non-Hodgkin lymphomas (NHL). In the United States, the median age of patients diagnosed with PCNSL is 55 years, with men more affected than women. Between 1973 and 1998, there were 2,502 patients with PCNSL reported in the Surveillance and End Results Reporting (SEER) database, with only 29 cases (1%) in patients under age 19 years. Based on the SEER data and census information, one could predict 10 to 12 cases per year of PCNSL in children and adolescents in the United States per year. The etiology of PCNSL is not clear. PCNSL is more common in patients with immunodeficiency, acquired or congenital, with PCNSL accounting for as many as 10% of cases of NHL observed in the HIV-infected population, though the incidence appears to be decreasing in the era of highly active antiviral therapy (HAART). Epstein-Barr virus (EBV) is often associated with B-cell PCNSL, and essentially all PCNSLs associated with immunodeficiency are EBV positive. Histologically, diffuse large B-cell lymphoma accounts for the majority of PCNSLs (90%), with Burkitt’s lymphoma rarely occurring and T-cell lymphomas accounting for 2% to 8% of cases. Clinically, PCNSL presents with mental status changes, focal neurologic deficits, or seizures. About 40% of patients have leptomeningeal seeding, whereas about 10% have isolated leptomeningeal involvement without a mass. Ocular involvement is common (ie, about 15% of patients), and isolated ocular disease without a CNS mass can occur. The standard evaluation of a patient with suspected PCNSL includes cranial MRI, a slit-lamp examination by an ophthalmologist, and acquisition of tissue through either craniotomy or stereotaxic biopsy. However, about a third of patients will have positive cerebrospinal fluid at diagnosis, which may obviate the need for craniotomy if a lumbar puncture can be safely performed. Data for treatment and outcome of PCNSL in children are largely based on reports for adult patients, though some series have included adolescents. Factors that have been shown to affect prognosis adversely in adults with PCNSL include age at diagnosis (.60 years of age), Eastern Cooperative Oncology Group (ECOG) performance status more than 1, elevated LDH, elevated cerebrospinal fluid protein, and deep brain involvement (basal ganglia, brain stem, cerebellum, and periventricular regions). The International Prognostic Index (IPI) is not helpful because the stage and number of extranodal sites is fixed. The presence of ocular disease at diagnosis and T-cell disease have not been found to have prognostic value. Long-term progression-free survival for PCNSL is poor. Steroids alone produce rapid but usually not durable responses. Whole brain irradiation (WBI) can achieve prolonged survival, but cures are rare. One report found that WBI of 40 to 50 cGy produced a 4%