Understanding Mammogram Over-Diagnosis

This video from H. Gilbert Welsh, the author of the recent controversial NEJM paper on mammogram screening, should be required viewing for every woman and her doctor. (HT to Gary Schwitzer for bringing it to my attention.)


Bottom line – three decades of mammogram screening has had only a modest impact on the incidence of late stage breast cancer, and leads to over-diagnosis and over-treatment of early stage cancers in return. Declines in mortality are modest, and can be attributed in large part to advances in breast cancer treatment.

Overall, mammograms are thought to lower breast cancer mortality by about 15-20%. Which ain’t nothing. But it’s a lot less than most people think.

If you want to see what a highly effective cancer screening intervention looks like –

Let’s look at pap smears and cervical cancer screening – in this case in the UK, where a nationwide cervical cancer screening program was introduced in the late 80’s. Note the dramatic decline in the incidence of cervical cancer resulting from screening and subsequent treatment of pre-cancerous lesions-

With a concomittent large decline in cancer mortality that has not been disputed (note how the angle of the decline drops significantly in the late 80’s when screening is introduced) .

What is not shown in these graphs is the sharp increase in precancerous cervical disease that went along with the decline in invasive cancer and later stage disease – exactly what you’d expect from a highly effective cancer screening intervention. Pap smear screening works because cervical cancer has a relatively long precancerous phase during which screening and treatment can be done to prevent progression to cancer. (Colon cancer screening works the same way).

Mammograms are just not working as well as pap smears and colon cancer screening works. Either they don’t find the treatable early or pre-cancerous lesion in enough cases to make the kind of impact we were expecting, or more likely, not all so-called “early” breast cancers are destined to progress or cause death if diagnosed later or left untreated. This is supported by the fact that increases in the diagnosis and treatment of DCIS (Ductal carcinoma in situ) has not led to much of a decline in later stage breast cancers in the same way that treating cervical carcinoma in situ prevents invasive cervical cancer and cervical cancer deaths.

We are beginning to think that there are different types of breast cancers – those that are slower growing and less likely to metastasize and kill, and those that are aggressive from the get-go. Screening tends to pick up the former (hence the term “over-diagnosis”) and miss the latter, since they grow and spread so quickly.

This does NOT mean that no woman should get a screening mammogram.

It is saying that we need to have a more realistic understanding of what mammograms can and can’t do, and supports the recommendation that we make make decisions about mammogram screening that are based on that reality.

It also will hopefully help to dispel the prevailing myth that if every woman just got a mammogram every year, there would be no deaths from breast cancer.  Sadly, that is just not true.  Mammograms do prevent some deaths from breast cancer.  But not all of them. And the price we pay for preventing the deaths we do prevent is over-diagnosis and over-treatment of some women who may never have died from their cancer in the first place.

The problem, of course, is that at  present we have no way of knowing which women we are over-treating and which women we are saving.

Until we can do so, we must and will continue to offer screening mammograms.

When to start that screening, and how often to have it, is the question each woman must ask and decide with her doctor.  Hopefully, videos such as this one will help in making those screening decisions informed and reality-based.

Recommended Reads

4 Responses to Understanding Mammogram Over-Diagnosis

  1. Thank you for posting this. This past spring I made the personal decision to stop annual mammograms, having had 3 false positive readings out of 6 of the annual tests. In my case I think I’m just particularly difficult to image at this stage in my life (late 40’s) and because I’m not in a high risk group, I do self-exams and I get an annual physical that includes a manual breast exam I feel it’s a pretty safe choice. Additionally, I’m not too keen on the annual dose of radiation – a worthwhile trade off for an effective test but perhaps not so much for a screening mammogram.

    I told my doctor of my decision and that I’d revisit the issue at around age 55. I will be interested to see what the prevailing wisdom is by then.

  2. Thanks for your take, Peggy. I agree that breast cancer is not a monolithic disease – some forms seem to be benign and even “curable” by the body’s immune system. Others are aggressive and metastasize very quickly. We can’t yet tell the difference by looking at a lump on a mammogram – so we over-treat. As we get better at understanding the different behaviors of sub-types of breast cancers our screening and treatment strategies will evolve. I’m opting out of screening – though I respect that many don’t wish to do so. My take is here: http://getbetterhealth.com/should-you-get-a-mammogram/2012.11.26

  3. Would that you had posted this a few months earlier, before my 3-D screening mammo found an irregularity that likely would not have been found on an older type mammo. I subsequently had a follow-up mammo, u/s, u/s-guided needle core biopsy with a mammo to check placement of the biopsy marker only to find that the mammo and the u/s each had found different “irregular spots.” Biopsy was benign, but I now needed both spots removed. Subsequently I had an MRI and then excisional biopsies/lumpectomy, removing both questionable areas (neither palpable, and fairly far apart within the same quadrant.)

    All was found to be benign, but not until I’d gone through all the procedures, suffered complications from the surgery that had me back in the OR 2 weeks later for a surgical evacuation and irrigation of the biopsied areas, plus placement of drains. And now, almost 3 months later (and 10 follow-up visits to my surgeon later) I’m still in severe pain, not fully recovered, with at least one more surgical f/u scheduled. I wish I had forgone the screening this year. I know once something was found, the doctors had to pursue it, but I wish it had never been found.

    This wasn’t an over-diagnosis, as no cancer was diagnosed, but a screening that has resulted in 10 weeks (still ongoing) of severe pain, both with mental and physical – for a couple of tiny oddities picked up by very high resolution mammography. We won’t even consider the $25,000+ in costs my insurance has had to deal with this.

    I think I’ll skip next year’s screening.

Leave a Reply