Is Cancer Progress Stagnating?

Epistemic Status: a best attempt to give my current understanding.

The War on Cancer began with the National Cancer Act of 1971, and continues to this day. The National Cancer Institute, the largest federally funded organization for cancer research, has a budget of $4.95 billion for 2015; the NIH’s total budget for cancer is $5.39 billion.

But the War on Cancer seems to have disappointing results. Cancer deaths have only fallen by 5% since 1950, at a rate of 200 deaths a year per 100,000 individuals.  (By contrast, heart disease deaths are a third of what they were in 1950, thanks to innovations like statins, stents, and bypass surgery.)

Let’s dig into the cancer numbers to see if this represents real stagnation in medical progress.  It’s possible, for instance, that we’re getting better at treating cancer and it’s just that more people get cancer in the first place, for lifestyle or environmental reasons.

Looking in more depth at the overall cancer numbers from the National Cancer Institute, we see that age-adjusted overall cancer mortality looks a bit better; a 15% decline since 1975, and a 22% decline from the peak of cancer mortality in 1991.  So it looks like cancer deaths were getting worse from the 1950’s through early 1990’s.

Incidence rates also showed a rise from 1975 to a peak in 1991 in males, and a continuing rise in females. Cancer incidence data is sparse before the 1970’s — US population-level data were collected only three times during a period of more than 30 years before 1973.  But cancer incidence was reported to have declined between 1947 and 1970. So the “stagnation” in cancer death rates from 1950 to the present is clearly somewhat confounded by the rise in cancer death rates between 1950 and the early 1990’s.

Now let’s subdivide into some common types of cancer.

Breast cancer has a solid 33% decline in death rates since 1975, beginning in the late 90’s, despite rising incidence.  (It’s one of the most common cancers, at an incidence of 130 per 100,000.)

Prostate cancer, at an incidence of 114 per 100,000, had incidence rise sharply from 1975 to the 90’s, and has been dropping since.  Death rates, likewise, rose and fell over the same timeframe, but are still 35% lower than they were in 1975.

Lung cancer, which has a current incidence of 41 per 100,000, rose dramatically in men to a peak in the early 90’s, and has been falling since; it is less common in women but steadily rising. (This may be a consequence of trends in smoking habits.)  Lung cancer deaths, like overall cancer deaths, rise to a peak in the early 1990’s and decline thereafter; there has been no overall change in lung cancer deaths since the 70’s.

Colon cancer, at 27 per 100,000, has had its incidence drop by 42% since 1985; death rates have dropped accordingly.

Melanoma, at 23 per 100,000, really does have stagnant death rates.

Non-Hodgkins Lymphoma, at 20 per 100,000, has death rates peaking in the late 90’s but no net change between 1975 and the present.

Kidney cancer, at 15 per 100,000, has been rising steadily in incidence since the 1970’s; death rates have been more or less steady. (Some of this may be due to earlier detection of less severe cases.)

Leukemia, at 14 per 100,000, has slightly increasing death rates

Pancreatic cancer, at 13 per 100,000, also has stagnant death rates.

Ovarian cancer, at 12 per 100,000, has declined somewhat in incidence since the 1970’s, and had a roughly comparable decline in mortality.

Cervical cancer, at 6.5 per 100,000, has more than halved in incidence since 1975, and has seen a comparable drop in death rates.

The overall peak and decline in cancer mortality seems to be an artifact primarily of lung cancer incidence, which tracks trends in smoking habits. Breast cancer is the only one of the most common types of cancer that looks like a strong “success story” for treatment — i.e. deaths dropped significantly faster than incidence. Childhood cancer is also a “success story” — deaths dropped in half while incidence slightly increased.  Then there are cases like colon and cervical cancer, where incidence notably declined, perhaps due to the rise in early screening. But on the whole, the figures seem consistent with the hypothesis that the “war on cancer” has not been successful.  In particular, if you look at our ability to treat cancer (as opposed to prevent it, through things like screening or anti-smoking campaigns) the progress looks worse than the raw death numbers would suggest.  (A life saved is a life saved, no matter the means; progress in prevention is a major humanitarian gain.  But it is in some sense less of a technological gain.)

The conventional hypothesis as to why cancer progress has been difficult is that cancer itself is complex and diverse and there is little low-hanging fruit.  “Simplifying principles may not exist”, says an NPR interview with leading cancer researchers. More specifically, the discovery of oncogenes in the early 1970’s led molecular biologists to believe that the onset of cancer was a single “switch” that could be turned off; instead there turned out to be a wide array of oncogenes and tumor suppressor genes, activated in no particular order, and resulting in a great diversity of phenotypes.

This “low-hanging fruit” explanation is the usual one given to explain phenomena like “Eroom’s law”, in which the number of new drugs approved by the FDA per dollar of research spending has steadily declined since 1950.  Biology is complex; progress is hard; that’s it.

The contrarian hypothesis is that cancer research is doing something avoidably wrong.  Usually proponents say something in the vein of “cancer research is too traditionalist” — conservative, slow to innovate, wedded to unsuccessful strategies.  One might assume that this is prima facie absurd — after all, with all the time, money, and human intelligence spent on cancer, if there was a cure out there wouldn’t somebody have found it?  Cancer researchers can’t all be idiots!

In subsequent posts I’ll try to argue that the “cancer isn’t hard” position is at least plausible. This really divides into a negative case — that there are systematic biases in medical research and treatment that push against making progress on cancer — and a positive case — that there are plausible candidates for radical innovation in cancer treatment that deserve more attention.  In an ideal world, this argument would be made by a science journalist or an experienced biologist; I am neither, and so I’ll simply present the facts I’m aware of, with the understanding that it’s pretty incomplete and somebody may come along later and either flesh it out or refute it.

Advertisements

7 thoughts on “Is Cancer Progress Stagnating?

  1. I’m a little confused by the comparison that’s happening here. We got really good at fixing heart problems and now people die of that less. People still eventually die, right? And they have to die of something. Maybe all those people who previously would have died of heart disease are now dying of cancer instead. Maybe those people are harder to treat because they are generally less healthy. Wouldn’t that make our cancer progress look bad, even if the typical person who died of cancer 50 years ago would have very good chances today?

      • I am skeptical that that is a sufficient correction. Note that people who would have died of other stuff 50 years ago but die of cancer today still have those other health problems. Their cancer may be harder to treat successfully.

  2. Can we assume that the incidence rate change is “real”? Take breast cancer, the success story. Part of the “war on cancer” was increased mammography screening. This means more diagnosis, which means more incidence; if you want to reduce mortality per diagnosis they are very good! But they may not decrease actual mortality at all. Of course, the 33% decline there is presumably some success anyway. I would worry that incidence rate changes are in large part about what we classify as what and how we screen, rather than about the actual cancers becoming more or less common.

    • Well, but absolute death rates (age-adjusted and per-population) went down. That at least argues that screening had a benefit, even if nothing but screening and early surgery was responsible for the effect. If we just detected more mild cancers, but didn’t improve at treating them, you’d see *five-year survival* rates go up (which is why survival rates are bullshit) but total death rates wouldn’t go down.

  3. It is tangential to your topic, but why do you credit reduced cardiac deaths to medical intervention? I suspect that nutrition and pollution play a greater role.

    You mention statins, stents, and bypasses. To that I would add blood pressure drugs. You credit them with the reduction from 1950, but they are all recent developments, covering no more than half that period. The surgeries are older than the drugs, but, as you said in a recent post, it is quicker to ramp up the use of drugs than the use of surgery. So I do not think that any of the population improvement from 1950 to 1980 can be credited to any of these interventions. Are there earlier interventions I have missed?

    As to the improvements from 1980, how much is due to these interventions? The magnitude of the effect seems too great to be plausible to me, but I have not made a quantitative study.

    • That’s a fair point and I haven’t looked into heart disease yet. I’ve heard that shifts in diet have made a difference; also smoking matters. There may be other factors I haven’t thought of.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s