A new review of the breast cancer screening ( mammography ) literature came out in the Lancet this week. This is essentially an expert panel reviewing old data – nothing new. The UK-based panel looked a the data from a number of long-running screening cohort studies and produced a set of round number estimates for the benefits, harms and rates of overdiagnosis. Here are their absolute screening vs no-screening comparison numbers:
- Screening women aged 50 – 70 would prevent 1 cancer death for every 180 women who actually underwent testing. This is an estimate derived from a heterogenous group of data packets.
- The relative risk of breast cancer specific (not all cause) mortality was ~ 0.8 (CI 0.73 – 0.89). So it appears to have a significant impact upon breast cancer specific mortality.
- Overdiagnosis is the concept that has generated a significant controversy with this new review. the Panel looked a the various trials and concluded that about 1 woman in 77 screened from 50 until 70 years would have an “overdiagnosed cancer” (just over 1 %) ie. a tumour that would have presumably not caused any illness for that woman if undetected.
- Of course massive population trials don’t tell you who has the true cancer and who has the “silent” cancer – so all of these women will undergo surgical procedures and some adjuvant therapy for what was not going to be a true disease. And there will be morbidity associated with this.
- In summary screening will prevent roughly one breast cancer death for every 3 women who get “overdiagnosed”.
- There was no mention of “all-cause mortality” – hence no way of saying the true mortality difference between sceened and unscreened women.
- The 2006 Cochrane review found no difference in overall mortality between screened and unscreened populations – so that is a bit of a fly in the ointment.
So where do the pink cricket bats come in?
For the international readers – one of the best fast bowlers of the modern era was Glen McGrath – he played for Australia and was like ametronome – accurate and bouncy. His wife passed away from breast cancer a few years back and he started a charity the McGrath foundation. Each summer our national cricket team put hot pink handles on their cricket bats to raise money for breast cancer research and specialist nurse training in the care of women with breast cancer.
Every time I get into a discussion about breast cancer screening there is always somebody who says it doesn’t have enough evidence and that it should not have such a high public profile. Seems like a fair point – should we be promoting something that doesn’t have a strong proven benefit. Well I think this is wrong.
What we need for this devastaing and common disease is more research into screening, prevention and treatment. The high profile of organisations such as the McGrath Foundation help with this research. Improved screening technology and more effective / less destructive treatment will hopefully result in a smaller NNT and greater benefit to women who are diagnosed with breast cancer.
The first cricket test starts later this week – Australia vs. South africa – so bring on the pink bats I say!
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