shows results from the observational studies based only on women with breast cancer.
Observational studies of women with breast cancer; the number of deaths or advanced cancers and relative risk of dying from breast cancer in women who practise BSE compared to those who do not and in those who found their cancer during an examination
shows the individual relative risk of death from breast cancer and the pooled relative risks. Overall, there appears to be a statistically significant 36% reduction in the risk of death (relative risk 0.64, 95% CI 0.56–0.73, P
<0.001) in those who practise BSE. There was no evidence of heterogeneity between the studies (P
=0.41). If the study in which some women had mammo-graphy (Huguley et al, 1988
) is excluded, the estimate is not substantially different (relative risk 0.69, 95% CI 0.56–0.85, P
<0.001). In those women who reported that their cancer was detected during self-examination, there was no evidence of a reduction in the risk of death compared to those who found their cancer by chance (relative risk 0.90, 95% CI 0.72–1.12, P
=0.34). Again there was no strong evidence of heterogeneity between the results (P
=0.26). If the study (Kuroishi et al, 1992
) in which some women had mass screening is excluded, the estimate is not much changed the pooled relative risk is 1.00 (95% CI 0.85–1.18, P
Figure 1 Observational studies of women with breast cancer, comparing the breast cancer death rates between the BSE and non-BSE groups. A test for heterogeneity between the studies yielded a P-value of 0.41 for those studies based on women who practise BSE and (more ...)
shows the relative risk of having advanced breast cancer in women who practise BSE compared to those who did not, among all women newly diagnosed with breast cancer. There is a 40% reduction in the risk (relative risk 0.60, 95% CI 0.46–0.80, P<0.001). Although there was evidence of hetero-geneity (P<0.001), all the studies reported a reduction in risk. In women who found their cancer during an examination, there was a 34% reduction in risk (relative risk 0.66, 95% CI 0.44–1.01, P=0.06).
Figure 2 Observational studies of women with breast cancer, comparing the rates of advanced breast cancer between the BSE and non-BSE groups. A test for heterogeneity between the studies yielded a P-value of <0.001 for those studies based on women who (more ...)
The results from the cohort and case–control studies of women with and without breast cancer according to BSE practice are shown in . The two cohort studies show inconsistent results; one indicates a statistically significant 29% reduction in the risk of death associated with BSE practice (relative risk 0.71, 95% CI 0.57–0.87) and the other shows no effect at all (relative risk 1.03, 95% CI 0.95–1.12). The pooled estimate is not statistically significant (relative risk 0.87, 95% CI 0.62–1.23, P
=0.42). None of the case–control studies found statistically significant effects with only one suggesting a benefit (Harvey et al, 1997
). The results for two of the case–control studies were not materially altered after adjustment for mammography use (Newcomb et al, 1991
; Muscat and Huncharek, 1992
Observational studies of women with and without breast cancer; number of deaths and relative risk of dying from breast cancer in women who practise BSE compared to those who do not
provides the main results from the trials of teaching BSE and shows the relative risks and the pooled estimates for the main outcomes. The nonrandomised trial in the UK showed no effect overall (relative risk 0.99) even after 16 years of follow-up, although there was a difference between the two BSE centres; one showing a reduction in mortality (relative risk 0.79) and the other not (relative risk 1.09), which cannot readily be explained.
Clinical trials of BSE; the number of biopsies, breast cancer cases and deaths and the relative risk of dying from breast cancer in women who practise BSE compared to those who do not
Trials of BSE training. The rates for specified outcomes are compared between women invited for BSE training and those who were not. A test for heterogeneity between the trials yielded a P-value of 0.94 in relation to the results on mortality.
In the Russian trial, twice as many women in the BSE group sought medical advice compared to the non-BSE group (), and this was consistent throughout the course of the trial (BSE vs non-BSE groups: 5.6 vs 2.8% at 5 years, 7.2 vs 3.5% at 9 years and 7.5 vs 3.8% at 13 years). After 10 years, the two trials (Russia and China) show that overall there were 53% more biopsies in women who were taught BSE compared to those who were not, this was highly statistically significant (relative risk of having a biopsy 1.53, 95% CI 1.44–1.63, P<0.001). The trials also suggest that at 5 years, women taught BSE were no more likely to be diagnosed with breast cancer than those not taught BSE (relative risk 1.01). After a longer follow-up (9–10 years), there is an indication from the Russian trial that more cancers were found in the BSE group (24% more women diagnosed with breast cancer), but this was not found in the trial from China.
The risk of dying from breast cancer was remarkably consistent between the three trials and over the different follow-up periods. There was no evidence of an advantage in the BSE group after any length of follow-up. The pooled relative risk was 1.01 with narrow 95% confidence limits (0.92–1.12, P=0.79); there was no evidence of heterogeneity (P=0.94). The results were not materially different if the nonrandomised trial from the UK was excluded, pooled relative risk 1.05 (95% CI 0.90–1.24, P=0.54).
There was little evidence that the effect of BSE varied between women in different age groups ( and ).