A couple of years ago, the American Cancer Society gaily reported that cancer survival rates have been improving dramatically and steadily. A few weeks ago, Cancer Research UK announced a similarly sunny prognosis for the public at large: UK survival rates have doubled in 30 years. Yes, we are all "surviving" longer with cancer, the experts can assure us.
What fabulous news this seems to be: people diagnosed today are twice as likely to survive for 10 years than people diagnosed 30 years ago. As the press release says: "While survival varies widely between different types of cancer, on average, a patient with cancer now has a 46.2 per cent chance of being alive 10 years after diagnosis. This compares with 23.6 per cent 30 years ago".
Now, what do you suppose that means? Do you imagine that treatments have improved so much in 30 years that we are actually able, on average, to slow the disease's rate of progress by half? That we have actually doubled the life expectancy of cancer patients? That certainly is one message that we might take from the press release.
Well, those who actually bother to read medical literature know that what is being claimed here is a bit less fabulous than that. In the field of medicine, words like "survival" and "cure" are professional jargon with specific meanings and implicit qualifications. Researchers and doctors know what these terms mean, and they use them very carefully, assuming the implied qualifications are understood. Unfortunately, you and I might understand something quite different from what is meant.
So, what do professionals mean when they speak of survival? Typically, they speak of five-year survival in a way that gives patients a decent guess of their chance of still breathing five years after diagnosis. The doctor considers the specific form of cancer, its state of progress at the time of diagnosis, the patient's overall health, age, sex, and numerous other factors, and then a comparison is made between the individual patient and a group of similar patients.
So, it's common for a practitioner to compare your current condition to a large group of others previously diagnosed in similar circumstances, and tell you, for example, that among those similar to you when they were diagnosed, 60 per cent survived for five years.
Thus you would have a 60 per cent chance of surviving for five years. You might also be told that you have, say, a 30 per cent chance of surviving disease free (i.e., in remission), and a 45 per cent chance of surviving progression free (disease is detectable but not worsening), for five years, based on comparisons with others whose conditions were similar to your own at the time of diagnosis. Thus, "survival", in the professional sense, is relative.
But if survival is a relative measure, what can it mean when Cancer Research UK says that survival rates have improved overall? What, exactly, is being compared to what in that case? Does it mean that we have got so good at treating cancer that the disease typically progresses at half the rate it once did? Does it mean that patients are actually living twice as long as they did 30 years ago? I do wish I could say this is so, but then I would tell a lie.