The effect of hysterectomies and screening on mortality from cancer of the uterus in Canada.

The trends in mortality from cancer of the uterine cervix, cancer of the endometrium and all uterus in Canada and the ten Canadian Provinces from 1951-53 to 1974-76 at ages 30-64 have been re-evaluated in relation to screening for cancer of the cervix in 1966 and 1971 and hysterectomies for non-malignant conditions from 1969 to 1976. By means of series of mathematical models, the effect of different prior extrapolations of the numbers of hysterectomies performed by age and province has enabled the potential impact of hysterectomies on the trends of mortality from uterine cancer to be evaluated by relating deaths to "uteri at risk" rather than "women at risk" irrespective of the presence of an intact uterus. It has been found that the numbers of hysterectomies performed have little impact on the fall in mortality certified to cancer of the cervix or to all uterine cancer, but in the decade 1964-66 to 1974-66 they convert an apparent fall in mortality from cancer of the endometrium to stability. Re-evaluation of the fall in mortality from 1960-62 to 1970-72 in relation to the intensity of screening shows little impact of the hysterectomies performed on the significant correlation reported previously. However, after extension of the analysis to 1974-76 the correlation disappears. This finding may indicate a more limited potential for the application of screening, as practised in Canada, to reduce mortality from cancer of the cervix, than has been anticipated previously.