Will primary central nervous system lymphoma be the most frequent brain tumor diagnosed in the year 2000?

There has been a dramatic increase in the diagnosis of primary lymphoma of the brain during the past decade, prompting speculation that it may become the most frequently diagnosed tumor of the central nervous system by the year 2000. The current analysis drew from the updated Surveillance, Epidemiology, and End Results (SEER) database to establish projections for the incidence of brain lymphoma. The study also attempted to determine whether increased incidence rates are attributable to the increasing incidence of acquired immunodeficiency syndrome (AIDS) and whether there is gender or age dependence.

Primary brain lymphoma case data and population census data for calculating incidence rates for the period 1973-1992 were obtained from the SEER program. In an attempt to determine the contribution of AIDS to the increasing incidence of the disease, separate analyses were performed with and without the inclusion of never married men (a high risk group for the development of AIDS). Separate analyses were also performed within the San Francisco SEER registry because a higher incidence of AIDS-related cancers has been documented in this geographic region. Finally, a piece-wise linear model (using one regression line until 1982 and another regression line from 1982 onward) was used to predict incidence rates for the year 2000.

During the period of study, the incidence rates of brain lymphoma increased more than 10-fold, from 2.5 cases per 10 million population in 1973 to 30 in 1991-1992 (chi-square trend, 17.76: P < 0.0001). These increased incidence rates were independent of age and gender. The incidence rates of primary brain lymphoma did not differ significantly when comparing the San Francisco registry with the remainder of the SEER database for any comparison that excluded never married males. However, when the analysis included never married males, a statistically significantly higher incidence rate of primary central nervous system lymphoma was observed among San Franciscans compared with age-matched controls from the remainder of the SEER database. In the year 2000, the projected incidence rate of brain lymphoma would reach 51.1 per 10 million population and 118.2 per 10 million population, with never married men excluded and included, respectively. These incidence rates would still fall below the corresponding projections for glioma and glioblastoma multiforme.

There continues to be a significantly increasing incidence of brain lymphoma that is independent of age and gender. Indirect evidence implicates the AIDS epidemic as a contributor to this trend. Although the rate of increase in the incidence of non-Hodgkin's lymphoma of the brain is higher than for peripheral non-Hodgkin's lymphoma and other glial tumors, brain lymphoma is not projected to surpass glial tumors as the most frequently diagnosed intracranial malignancy by the year 2000.