As background, in 2009 an expert panel recommended that screening mammograms not be started until age 50 for women at average risk (that is, those who do not have some characteristics that create higher risk of cancer and thus suggest more aggressive screening). The panel was headed by a former colleague of mine when I was at University of Texas Medical School (she is now at Baylor), Virginia Moyer, one of the smartest and clearest thinking scholars of medical policy I have known. Their recommendation was undoubtedly right – I base that not just on trusting Moyer, but also on my own expertise on this topic. The costs of screening a low risk population, like those aged 40-49 are enormous. We pay for the direct costs of the mammograms themselves, and the huge costs of further invasive testing (to confirm that most of the positive mammograms were really false positives) and treatment (which is often unnecessary – see below), and the patients suffer from the lost time and pain from the millions of mammograms, the fear created by false positives, and invasive procedures.
Moreover, it is quite plausible that screening at age 40, when cancer risk is very low and the breast tissue is difficult to see through, is more likely to cause cancer than to help cure it. That is, the ionizing radiation from the mammogram has some risk of causing cancer, and since screening drops in value as the women gets younger, at some point it must be that the risk is actually greater than the benefit (e.g., mammograms for 20-year-olds are of basically zero value, but still create a risk from the radiation). I am not expert in the risk from the radiation, but back when I worked in this area, someone who I was inclined to trust estimated that age 45 was the time when this crossed over, and the benefit exceeded the risk (and notice that this considers only cancer risk, not all the other downsides of screening, testing, and treatment).
In short, doing mammography too early or too often (the new guidelines also said every two years, not every year) is expensive in many ways. It is therefore important to put proper limits on how much is done to avoid creating excessive expense, misery, and actual disease risk. Not so, according to the story touted by the
The sales pitch included results from two studies (I use that phrase charitably). The first found that following the publication of the 2009 guidelines, screening of women aged 40-49 went down. Good news, right? A sensible guideline is created and people start following the guideline. Not according to the radiologists, since this is "possibly negatively impacting on the benefits of prompt detection." Well, we cannot have that, can we? Saving zillions of dollars and needless trauma is no good if it possibly negatively impacts something to an unknown degree.
Actually, if they had been referring to screening less frequently at older ages, it would have been undoubtedly the case that there was some negative effect due to the reduction in detection. That loss would be warranted by the reduction in other costs (according to the guidelines), but clearly more screens means more detection, ignoring all else. However, for the under-50 age group, the radiation effect means that it is actually conceivable that the cancer benefits of not doing the screens is actually positive. To my knowledge, we do not know for sure.
The second study touted to the press claimed:
Cancer diagnoses among 40-49-year-old women who had undergone screening mammography occurred at a much earlier stage of the disease compared to women of the same age who had not undergone screening.Well, yeah. The rare cases of serious cancer in this age range are caught, absent screening, because they advanced to a stage that can be detected due to a lump or other symptoms. But contrast, most of the cases detected by mammography are very small and of a type that might never become serious. That is, many of the cancers that are detected never would have turned into a disease, but the medics who detect them will claim credit for intercepting and curing a disease that never would have happened. (This phenomenon is know as "over-diagnosis". I explained it in detail in UN84, along with the concept of "lead-time bias". If you are interested in fully understanding my points today and are not familiar with those, I suggest reading that.)
Also it is not clear how much worse the outcomes are for cases that do advance because they are not caught by under-50 screening, to be detected and treated later. Worse, no doubt, but it is difficult to know how much worse because it is difficult to sort the successful treatments that prevent the need for a later-stage treatment from the "successful treatments" of the cases that never would have been bad. It becomes especially difficult to perform this complicated analysis when you like the answer better when you do not bothering with it. After all, who is going to call you out for doing an analysis that is known to be incorrect? The health news reporters?
Further complicating the situation is that women who are doomed to die from breast cancer, but are detected by screening at age 45 rather than 55 will "survive" ten extra years even if they die at the exact same time. The screening will be credited with providing a benefit even though it merely started the clock sooner (this is lead-time bias).
Yes, it is possible that the radiologist researchers properly adjust for these challenges, but it seems unlikely. Certainly the quotes that showed up in the news strongly suggested they were completely ignoring them. Frankly, even though they live in that world, my experience suggests that they may not understand these problems. Physicians as a group (with obvious exceptions like Ginny Moyer) strike me as less able to understand these points than average college educated and numerate people (UN84 was motivated by an economist instantly understanding and clearly articulating lead-time bias, something that takes a very long time to explain to medics). Perhaps this has to do with the classic explanation, that their paychecks benefit from them not understanding it. But blaming simple venal conflict of interest might be letting off too easy those who make claims like:
It's very important that we continue to do all that we can to catch breast cancer in the earliest stages so that we can continue to save lives.Isn't it interesting how much the "arguments" for screening at age 40 and annually are the exact arguments that could be used in favor of starting at age 25 and screening every month. Basically they say "if you ignore all of the health, psychological, and resource costs of screening, false positives, and unnecessary treatment then doing more screening is a good idea". Actually, I think I am letting them off the hook a little too easily with that "25 and every month" thing. The "we must do everything we can" claims often imply that every woman who is not expecting to nurse a baby in the future should get a double mastectomy. That will shut this breast cancer problem right down, and stopping breast cancer is worth any cost, right? Or is that only if the radiologists are the ones scoring in the profits?
Dear Carl,
ReplyDeleteThe words you write would have authorized my death sentence. Age 46, lymphnode positive with no family history ....my cancer was not able to feel but found with routine mammogram. I don't smoke, don't eat meat and exercise regularly. I would not have lived long enough to see a first mammogram at age 50.
Debbie, Sorry to hear about your health problems. I was not actually involved in making the policy. As I pointed out, screening at 46, or at 25, will catch some cases. That does not make it a good idea. Even setting aside the unknown number of 46-year-olds who were given cancer because of their mammograms, we should not do everything that has some benefit for someone sometime. It costs billions to screen every 40-something-year-old every year.
ReplyDeleteOne reason that we make policy based on population statistics and not individual case reports is that we never actually know, in a particular case, what would have happened under a different regimen. Another is that "policy by exception" makes for bad policies. There are people who are absolutely sure their lives were saved by not wearing a seatbelt, but the statistics show that making policy based on this would be unwise.
Finally, fwiw, the statistics do not show that smoking or eating meat has a substantial effect on breast cancer risk, and exercise seems to be modest (apart from the effect on BMI).