Hodgkin's disease in a national and hospital population: trends over 20 years.

The aim of the study was to investigate the incidence rate and time trends in a national registry population of Hodgkin's disease (HD) and the effects of selection in a hospital population. A national registry population of all HD patients from Norway and a hospital population of HD patients treated at the Norwegian Radium Hospital (NRH) were studied retrospectively from 1971 to 1993. The incidence of non-Hodgkin's lymphomas (NHL) in Norway increased steadily from 1961 in contrast to a stable incidence pattern for HD before 1980 and a decreasing incidence since 1980. Due to improved diagnostic tools after 1980, an increasing proportion of patients previously diagnosed as lymphocyte depleted and unclassified HD were classified as NHL. As these histologies are dominant in older patients, the incidence of older patients with HD and the total population of HD have decreased since 1980. As a result, the proportion of young adults with a favourable histology has increased. These changes may partly explain the increased patient survival observed both in the national and the hospital population. The hospital population comprised 92% of patients aged 15-39 years, 80% of patients aged 40-59 years and 53% of patients aged > 60 years in the national population. The selection of younger patients in the hospital material may explain a higher survival rate as compared with the national population.