Is primary CNS lymphoma really becoming more common? A population-based study of incidence, clinicopathological features and outcomes in Alberta from1975 to 1996

Background. The incidence of primary CNS lymphoma (PCNSL) is believed to be increasing in immunocompetent patients but this may not be universally tru e. The objective of this study was to determine in a population if the inci dence of PCNSL is increasing, if the histologic subtypes are changing, and to describe the clinicopathologic and outcome characteristics of PCNSL. Patients and methods: We identified all Alberta residents with a histologic diagnosis of PCNSL from 1 January 1975 to 31 December 1996 using the Alber ta Cancer Registry. Annual age-standardized incidence rates (ASIR), clinico pathologic and outcome characteristics were determined. Results. There were 50 immunocompetent PCNSL patients; the median age was 6 4 and 30 were male. Their median survival was 10.15 months. Histology was a vailable for review in 37 (74%) patients: 19 (51%) were diffuse large cell, 16 (43%) were immunoblastic and 2 (5%) were unclassifiable malignant lymph omas. The ASIR ranged from 0.178-1.631/10(6) and no change in ASIR was foun d (test for trend, P = 0.26) for gender or age. The ASIR of malignant gliom as did not change either but increased for all other non-Hodgkin's lymphoma (94.95-138.7610(6); test for trend, P = 0.0001) The number of brain biopsi es increased from 1979-1985 (test for trend, P < 0.0001) but remained stabl e from 1986-1996 (test for trend, P = 0.99). Conclusions: Unlike several other populations, PCNSL is not becoming signif icantly more common in Alberta. If this difference is real (i,e., not due t o differences in cancer registry coding practices etc.) comparisons between Albertans and other populations in whom the incidence is rising may provid e clues regarding the etiology of PCNSL.