THE INCIDENCE AND EPIDEMIOLOGY OF PLASMA-CELL NEOPLASMS

Plasma cell neoplasia includes monoclonal gammopathy of undetermined s ignificance (MGUS), multiple myeloma (MM), and Waldenstrom's macroglob ulinemia (WM). In MGUS, a large, stable clone does not cause symptoms; additional change(s) is/are required to convert this clone into a pro gressively expanding tumor that becomes symptomatic, as in MM or WM. T he prevalence of MGUS (i.e., the number of cases in a defined populati on at a certain time) is 20 times greater than MM. The incidence (i.e. , the number of cases developing in a defined population in a defined period) has not been determined for MGUS. Between 1960 and 1969, the a verage, annual, age-adjusted (1950 standard) incidence of MM in Malmo, Sweden was 3.4/10(5). The incidence of MM is strongly influenced by t he age and race of the population, and the diagnostic services availab le. MM is a disease of old age; it rarely occurs before the age of 40. The incidence of MM increases rapidly with age, is lowest among the C hinese and Japanese, intermediate among Caucasians in America and Euro pe, and highest among blacks in the USA. The striking differences in t he incidence of MM in different countries appears to be due to racial rather than environmental differences, since the low incidence among t he Chinese and Japanese in Asia has migrated with them to the Bay area of California and to Hawaii. The high incidence of MM in USA black ma les (10.8/10(5)) and females (7.2/10(5)) is more than twice the rate f or whites in the same regions. A striking increase in MM mortality rat es has been noted in many countries between 1968 and 1986. There is mu ch debate about whether this increase is real, or the result of steadi ly improving case ascertainment. Epidemiologists have not firmly ident ified any hazardous materials that increase the risk of developing MM. Previous evidence suggesting that radiation and benzene may play a ro le in the pathogenesis of MM has been greatly weakened by subsequent f ollow-up studies. Marked differences in the incidence of spontaneous M GUS in inbred strains of mice, differences in the susceptibility of th ese mice to the induction of plasmacytomas by the intraperitoneal inje ction of mineral oil, the racial differences previously mentioned in t he incidence of human MM, the association of MM with the HLA Cw2 allel e, and the familial occurrence of MGUS, MM and WM, suggest that geneti c factors are important in the genesis of plasma cell neoplasms. Chron ic antigenic stimulation (GAS) has long been thought to play a role, b ut epidemiologic studies have only established an association of MM wi th rheumatoid arthritis.