Having cancer for longer
The Dominion Post says “More Kiwis are winning the battle with cancer, with fewer people dying once they are diagnosed.” Obviously that’s not literally true: the number of deaths per customer is pretty convincingly fixed at one. What they seem to mean is that people with cancer are surviving longer. This might be true, but the underlying research, unfortunately, doesn’t really show it.
The Otago researchers studied survival time from diagnosis, and showed that it is increasing for many cancers. That is, Kiwis are spending more time having cancer than they used to. Survival from diagnosis involves two points. Moving the time of death later will increase survival, and is a Good Thing, but moving the time of diagnosis earlier without changing the time of death will also increase survival, and doesn’t do anyone much good.
What’s actually happening will be different for different cancers. For example, in breast cancer we know from randomized trials that both phenomena are occuring. Mammography makes diagnosis happen earlier for everyone, and this results in postponing death for many women.
For solid evidence of improved survival in cancer, you really need to look at something like mortality rates per 100,000 population per year, where there isn’t a problem of moving the goalposts.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
Firstly, “More Kiwis are winning the battle with cancer, with fewer people dying once they are diagnosed” is clearly intended to say “More Kiwis are winning the battle with cancer, with fewer people dying *of that cancer* once they are diagnosed”. Clearly there is not one per customer of those.
Secondly, you’re assuming that once a body has a cancer, it has it for the rest of its life. I’m pretty sure that that is false. What about tumours that get completely removed? Or people who are declared to be in remission? These are ways to win against cancer – people with cancer surviving long enough to become people without cancer again.
13 years ago
“fewer people dying *of that cancer* once they are diagnosed”. Actually, if you have cancer and die, your cause of death is very likely to be recorded as that cancer, regardless of the precipitating event. Probably for that reason the report didn’t look at cause-specific mortality, it looked at all-cause mortality. Their figures do include people who get hit by buses while in remission.
We know that there has been real progress in cancer treatment. Some cancers get genuinely cured (eg, many childhood cancers, Hodgkin’s lymphoma, testicular cancer). For others, such as breast cancer, we know that treatment really improves survival, but doesn’t completely get rid of the excess risk. The point is that we can’t tell from the report what the contribution is of cure vs lead-time bias. The headline could be true or not, but the story does not provide evidence to support it.
The reason we know, though, it is the population mortality data and the randomized trials, not analyses of survival from diagnosis. It’s just too hard to disentangle lead-time bias from genuine survival improvements.
13 years ago
Hi Thomas, enjoying the blog and nice to have you in New Zealand (please accept a belated general thanks for the survey package).
The problem of using survival rates as a proxy for the effectiveness of health systems is a fair cop, e.g., , but I think the Cancer Trends team have done better than that.
By analyzing changes over time in excess mortality for disease sufferers against a matched disease-free population (if I’m scanning this correctly, their EMRR) they really appear to be getting at improvements to care, over and above earlier diagnosis.
I was also preparing to go gangbusters on the dom piece, perhaps as a first entry to the stat of the week; but on reflection I just wish they focused on mortality in the title, and the press.
13 years ago
Oops no links, huh.
The e.g., was to The Incidental Economist blog who’ve a long and fertile discussion on survival vs mortality rates under the survival-rate tag.
13 years ago
Thanks Thomas for your blog I also found it very interesting.
I have been involved in the insurance industry for the last 12 years & with my company BRAVEday we have seen a real trend for people to insure themselves to receive assistance from insurance upon diagnosis (Trauma cover) & not at time of passing.
I have experienced this very close to myself when my mother was diagnosed with stomach cancer about 4 1/2 years ago. She received a lump sum payout literally 1 week after diagnosis equal to about 2 or 3 year living expenses. This made a major difference to not only my mothers life while she was alive (she survived 16 months before passing away) but also the people around her.
This experience I had has really shaped the advice I now give to our clients about where to be best spending their money on insurance type products … get assistance when you are still alive not only when you pass. Your blog just backs this up further to me
13 years ago