PARITY AND CANCERS OF THE GALL-BLADDER AND THE EXTRAHEPATIC BILE-DUCTS

The relation of parity and age at first birth to cancers of the gall b ladder and extrahepatic bile ducts in women was studied using a databa se generated by linking 2 Swedish national registries; the Fertility R egistry and the Cancer Registry. Among women born between 1925 and 196 0, 257 cases of gall-bladder cancer recorded in the Cancer Registry be tween 1958 and 1984 were compared with 1,285 controls, age-matched to cases in a 5:1 ratio. In addition, 60 cases of extrahepatic-bile-duct cancer were matched with 300 controls. There was a positive associatio n between number of live births and risk of gall-bladder cancer (p 0.0 6), but simultaneous consideration of parity and age at first birth re vealed a more complex picture. Parity increases the risk for cancer of the gall bladder when the first birth occurs before the age of about 25 years, whereas parity associated with first birth after the age of about 30 years is associated with reduced risk for the disease. Thus, among parous women there is a highly significant inverse association o f age at first birth with risk for gall-bladder cancer after adjustmen t for number of live births. Variable levels of pregnancy estrogens ac cording to maternal age and variable effects of parity on non-pregnanc y estrogens by age, may explain the observed pattern. The results on e xtrahepatic-bile-duct cancer, parity and age at first birth did not in dicate the existence of an association in either direction. (C) 1993 W iley-Liss, Inc.