European Breast Cancer Conference, Vienna, March 2012
Effectiveness of breast cancer screening
Rianne de Gelder – Erasmus University Medical Center, Rotterdam, Netherlands
Good morning everyone. I would like to present to you the results of our study on the effects of population-based mammography screening that starts before age 50, at ages between 40 and 50, and we compare that to the effects of adjuvant systemic therapy.
We will focus on breast cancer screening in the Netherlands. In the Netherlands we’ve had a screening programme since 1990 and we invite women aged between 50 and 75 at bi-annual intervals. The last couple of years we have shown in the Netherlands that breast cancer screening is very effective. Two case control studies showed that in screened women a breast cancer mortality reduction of more than 50% can be obtained and in women aged 55 – 79 years old a breast cancer mortality reduction of almost 31% can be achieved.
However, there have also been very many debates on the effects of breast cancer screening. For instance Kalager from Norway observed a 10% reduction in breast cancer mortality and they found that only one-third of this 10% reduction is related to screening and two-thirds of this reduction can be attributed to other causes like improvements in therapy such as adjuvant therapy. So this leads us to the question does breast cancer screening reduce breast cancer mortality or is adjuvant therapy nowadays so effective that the effects are as large as that of screening?
A second question which I would like to address in my presentation this afternoon is what are the additional effects of breast cancer screening before age 50? As I said, we currently start screening at age 50, as in many other European countries but what would happen if we were to start earlier? One of the reasons that we ask this question is that we see increasing incidence, a gradual increase in breast cancer incidence, over the last couple of decades which could mean that also the effects of screening may potentially become larger. In our analysis we will also take the effects of adjuvant therapies into account because they may interact with the effects of screening.
For our analysis we used micro-simulation model MISCAN and this model, I won’t explain this for you in very much detail, but it includes data on the screening as currently performed in the Netherlands and it also includes the data on adjuvant treatments such as endocrine therapies, chemotherapies etc. and it also includes all the observed incidence trends, screen detector rates, cancer rates that are screen detected, interval cancers etc. With this model we can predict breast cancer mortality, we can predict it with and without treatment and we can predict it with and without screening.
Let’s move on to the results. Here you can see the predicted breast cancer mortality in women aged 0 to 100, so we include some women that have never been invited to screening. The grey dotted line, the highest line, is the predicted breast cancer mortality in the absence of screening and in the absence of adjuvant treatments. The black dotted line is the predicted breast cancer mortality in the absence of screening but in the presence of adjuvant treatments, so the difference between those two lines is the effect of adjuvant treatments such as currently practised in the Netherlands, and the solid black line is the predicted line with adjuvant treatment and with screening, so the difference between the two black lines is the screening effects. As you can see, the effect of adjuvant treatment is 13.9% and the effect of screening, such as currently practised in the ages 50-75, is 15.7%.
What would happen if we add ten more additional screening rounds? We would start at age 40 then have ten annual rounds and then continue with the normal programme. Also with the model we predicted what would happen then and we see an additional reduction of the breast cancer mortality by 5.1% in again the age group 0 to 100.
So to summarise, the adjuvant treatment effect such as currently done, or the treatment that is currently done in the Netherlands, leads to a reduction in breast cancer mortality by 13.9%; screening such as currently performed leads to a reduction of somewhat higher, 15.7%. If we would then add one screening round, I didn’t show you that before, but one additional screening round would further reduce the number of breast cancer deaths by 1% and ten extra screening rounds would further reduce the number of deaths by 5.1%. So thank you very much.