I thought a brief explanation about survival rates might be helpful.
Before I started working in the health service, I had no idea what the concept meant. I figured it meant you either lived for ever or you died. But on joining the health service, I learned pretty quickly.
An 80% survival rate doesn’t mean that eight of ten people will live for ever and a day after being diagnosed with X illness or disease. It refers to a five-year period. Not that you will necessarily live out your so-called normal life until 70 or 80 or 90 or whatever. Just that you have a good chance of being alive five years after diagnosis. And that doesn’t even get into the issues of reoccurrence or metastatic cancer for example.
I must say as with a lot of communication, the NHS (UK health service) has improved its presentation of statistics. You can actually look up five year survival rates for cancer. – Here for anyone interested. If you look at that cursory weblink, you will note that breast cancer survival rates are above 80% which is a good thing. Similarly the rate for testicular cancer is 97% and prostate cancer is 80%. Malignant melanoma is between 80 and 90%.
Why then are people jumping on bandwagons to promote our awareness of any of those cancers?? Pancreatic cancer has a survival rate of less than 4%. Liver cancer is similar – the graphs I looked at didn’t mention the rate and also used one year survival rates because they look better. Lung cancer is around 8%. As is oesophageal cancer. Stomach cancer – 15%. Ovarian cancer is one of the baddies too but that is a whopping 40 odd %. Colorectal is one of the three ‘common cancers’ along with lung and breast. The survival rate for colorectal is just over 50% – that is really poor. When do we hear about any of those cancers??
Pause for a quick anecdote. We sold one of our houses to a medic. An eye surgeon. He had a Land Rover so mostly Partner and he talked Landies. But at some point they flipped onto a clinical discussion and Partner pointed out that survival rates were based over a five year period. Eye surgeon/Landy friend was bemused and asked how Partner knew that. Pretty obvious really given the fact I was responsible for cancer services. Then ‘Well yes but not many people know that.” Maybe not, but they should. Telling people they have a survival rate of 80% or 20% or whatever – without telling them it is over five years is downright misleading. The Mayo clinic – as ever – has a good and clear article here.
Now, while I am on about survival rates, I need to mention lead time bias. I was rather up on this at one point and could quote every relevant piece of research under the sun. Put very simply – lead time bias is about the difference between the start of your illness and when it is diagnosed or discovered, and the perceived impact earlier detection has on survival rates. Actually for once, Wiki puts it incredibly well. Check it out here.
Basically for example, if you are diagnosed with breast cancer from the screening programme, you may well find out that you have cancer sooner than you would if the cancer was diagnosed when symptoms appeared (normally small lumps in the breast/axilla areas). When the cancer is diagnosed doesn’t affect the overall life expectancy (and therein lies a whole issue about waiting times) but it can skew survival rate figures if it is detected early. If you are diagnosed earlier – you may well ‘appear’ to live longer. But life expectancy isn’t or shouldn’t be dated from diagnosis, it is from when the disease starts. There is a huge difference there. Anyway, check out the Wiki link because the diagram on there explains it very simply. Wiki also points out the additional impact of mental anxiety of earlier diagnosis.
Let’s go back to survival rates and lead time bias. For women diagnosed with breast cancer in 2001-2006, five-year relative survival rates have reached 82% (England only) compared with only 52% thirty years earlier in 1971-75. Ten year survival rates for women diagnosed with cervical cancer have improved from around 46% in the 1970s to 64% for the latest period.
Lead time bias anyone given the screening programmes??