SURGICAL-PROCEDURES ASSOCIATED WITH RISK OF OVARIAN-CANCER

Background. This historical cohort study was conducted to examine the relationship between gynaecological surgery and ovarian cancer risk. M ethods. Women were included ii they had had tubal ligation, hysterecto my, or unilateral ovariectomy in Ontario between March 1979 and April 1993. The cohort was linked to the Ontario Cancer Registry and the Ont ario mortality file. Person-years in the cohort were accumulated until death, the removal of both ovaries, a diagnosis of ovarian cancer, or the end of the study period 31 December 1993. Observed cancers were c ompared to expected based on Ontario age- and calendar period-specific incidence rates. Results. For tubal ligation and hysterectomy, fewer ovarian cancers were observed than were expected by age, calendar year of procedure, and length of follow-up; the observed/expected ratios w ere generally statistically significant. In contrast, no protective ef fect was evident for unilateral ovariectomy; in fact statistically sig nificant excess cancers were seen in early fellow-up periods. Observed /expected ratios were nearly identical and somewhat protective for the two strata defined by whether or not the ovaries were visualized. Dis ruption of the ovarian pathway conferred a protective effect, while no disruption significantly increased risk. Conclusions. The data do not support screening bias although short-term follow-up data indicate th e possibility of detection bias. The long-term follow-up data, as well as the data on pathway disruption, are consistent with the hypothesis that the surgical procedures themselves may produce a protective effe ct against ovarian cancer, through alteration of the hormonal environm ent and/or by physical destruction of a carcinogen's route to the ovar y.