Liver cancer in an endemic area of schistosomiasis japonica in Yamanashi Prefecture, Japan.

In Yamanashi Prefecture, schistosomiasis japonica has been endemic since the 16th century. Control of the disease has been very successful and no new case has been reported since 1977. Research has been conducted on the relationship between schistosomiasis and liver cancer, but no definite conclusion has been reached. We carried out several studies on this subject from the viewpoint of epidemiology. A descriptive study showed a higher mortality rate for liver cancer in the endemic area of schistosomiasis than in the country as a whole, but not much difference from the mortality rate in the non-endemic area. A case-control study showed a high odds-ratio for cases with a history of schistosomiasis; however, the value is almost the same as for cases which had hepatitis B (HB) antigen. This study suggested a multiplicative effect of HB antigen, history of schistosomiasis and history of alcohol intake. A retrospective cohort study showed a significantly high mortality rate for liver cancer in male inhabitants of the endemic area. These results confirm that schistosomiasis was closely related to liver cancer. However, the follow-up study of liver cirrhosis showed no difference in the survival curve and death rate from liver cancer between schistosoma positive cases and negative cases. A cross-sectional study of the prevalence of HB virus showed a higher rate in inhabitants with a history of schistosomiasis than those without such a history. Although the above two studies were carried out in small samples, it is considered now that schistosomiasis is one of the co-factors of liver cancer and indirectly associated with it.