Hodgkin's Disease Type Helps Explain Geographic Variation In Survival

MILAN, Italy, June 12 - Variations in morphology categories may help explain why Hodgkin's disease prognosis seems to differ from place to place from country to country, according to a study here.

The study also confirmed that - while the combined odds of five-year survival are about 80% no matter where a patient lives - some types of the disease have a markedly better prognosis than others, according to Claudia Allemani, Ph.D., of the Istituto Nazionale per lo Studio e la Cura dei Tumori here.

Reporting in the June 12 online issue of Cancer, Dr. Allemani and colleagues said their study provides "population-based evidence that morphology strongly influences the prognosis of patients with Hodgkin's disease."

However, they continued, "differences in the morphologic case mix explain only some of the geographic variations observed in survival."

In general, five-year survival - based on the Surveillance, Epidemiology, and End Results (SEER) database -- is about 83% in the U.S. In Europe - based on the results of the EUROCARE-3 study - the comparable rate was 78%, the researchers said.

However, there was considerable variation in Europe - from 62% to 88% -- among countries. In an attempt to understand why, Dr. Allemani and colleagues analyzed data on 6,726 patients diagnosed with Hodgkin's disease from 1990 through 1994 in 37 of the 67 population-based cancer registries that participated in EUROCARE-3 and 3,442 patients diagnosed with Hodgkin's disease over the same period in nine U.S. cancer registries that are part of the SEER database.

The researchers grouped the European cancer registries into three groups on geographic lines - EUROCARE West, EUROCARE UK, and EUROCARE East. The SEER registries were considered together, because their data were considered relatively homogenous.

The patients were grouped in five morphology categories, Dr. Allemani and colleagues reported - not otherwise specified, mixed cellularity, lymphocyte depletion, lymphocyte predominance, and nodular sclerosis. - and were also broken down by age.

Analysis found that overall survival was 80% in EUROCARE West, 77% in EUROCARE UK, 75% in EUROCARE East, and 83% in SEER.

The highest survival rate in all areas was for patients with lymphocyte predominance, followed by nodular sclerosis. The lowest survival rates were for lymphocyte depletion, with mixed cellularity and not otherwise specified having intermediate survival rates.

With one exception, there were no differences between the geographic groupings in survival within each morphologic group; the exception was that patients with lymphocyte predominant morphology in EUROCARE UK had significantly longer five-year survival than those in other groupings.

The key finding, Dr. Allemani and colleagues reported, was that patients in two areas - EUROCARE UK and EUROCARE East - had a significantly higher excess risk of death than those in the U.S., in a model that included years since diagnosis, age at diagnosis and gender.

The relative excess risk for EUROCARE East was 1.39 (with a 95% confidence interval from 1.21 to 1.60) and for EUROCARE UK it was 1.15 (with a 95% confidence interval from 1.04 to 1.28). The risk was non-significantly lower for EUROCARE West.

However, when the researchers adjusted for morphology, the relative excess risks didn't change substantially for EUROCARE East and West, but the difference between EUROCARE UK and Seer disappeared, Dr. Allemani and colleagues discovered.

The conclusion, the researchers said, is that the mixture of cases of different morphology accounts for much of the geographic variation in survival rates for patients with Hodgkin's disease.

But because not all the differences vanished when morphology was considered, "it is likely that differences in type of treatment and disease stage at diagnosis also contributed," the researchers said. "In particular, more advanced stage at diagnosis and less adequate treatment may explain the worse outcomes in EUROCARE East."