To screen or not to screen

Something I discuss with friends and family occasionally is the risk / benefit balance when it comes to making decisions about things like mammograms or prostate cancer screening. This post is about screening for people with no known risk factors – people with serious family histories are a different kettle of fish.

The fact that screening might sometimes do more harm than good is a concept that’s only just getting into public discourse in a major way. In my own experience doctors don’t tend to present this side of things to patients – I’ve never had cervical cancer screening presented to me as being optional, for example, simply as something that I’m expected to have. I’ve never had a discussion with a doctor about the potential risks or harms of screening, or even had a doctor acknowledge that there are any. Ditto with sexual health screening. I suspect conversations about mammography, prostate, and colon cancer screening are similar.

Conversely, research shows that people dramatically over-estimate the benefits of screening in terms of their risk of advanced cancer, and their risk of death. Even doctors are often unaware of how high the risks of false positives can be with some tests, and might treat all patients with a positive test as though they’re definitely sick, which causes emotional distress and may require unnecessary treatment. At the extreme end of this is the bad side of prostate cancer screening, where men undergo invasive surgery with potentially serious, long-term effects on their sexual function and their urinary continence for cancer that might never have caused them any serious harm.

Recommendations around prostate cancer screening are changing, in recognition of these harms. I suspect that mammography guidelines will change in the near future as well. Australia is going to move to five-yearly rather than two-yearly cervical cancer screening, as well. My hope is that eventually, cancer screening will be approached more in the way that genetic testing is – as a complex decision with risks and benefits, which individual patients need to weigh up for themselves with the help of a doctor, rather than under the instruction of one.

If you participate in cancer screening, this is something you could discuss with your GP. Questions to ask are along the following line:

  1. What’s the risk of me getting this type of cancer, at my age? How serious is that type of cancer – what proportion of people who get it die within five years?
  2. What does the test involve? Is it uncomfortable or painful?
  3. What’s the likelihood that I will test positive? If I do, what would that mean?
  4. If I tested positive, what would the next steps be? What other tests of procedures would I have to have?
  5. What are the risks and the down sides of those procedures?

So for example, for a woman in her thirties, the risk of cervical cancer is about 1 in 10,000 in any given year, and 1 in 60 over her entire life. About 20% of women who do get cervical cancer will die of it. The risks for women who have been vaccinated will be lower. Abnormal pap smears indicating possible pre-cancerous changes are much more common, and if this finding is confirmed by a biopsy, require a surgical procedure to remove the abnormal tissue from the cervix. Cervical biopsies and surgery are about as great as they sound, although the surgery is normally done under general anaesthetic.

These questions might throw your GP, but this is a conversation that your GP should be capable of having, and it’s reasonable to expect to have it before you take a test. Screening is a procedure you’re offered for your own good – it shouldn’t be something your doctor twists your arm into accepting. The evidence for mammography and especially prostate cancer screening is quite weak – if you’re considering having these tests, you should have a detailed conversation with your doctor so you both understand the risks and benefits, and how these gel with your values and preferences.

These are also questions it doesn’t hurt to ask about sexual health screening. A lot of GPs take a “test for everything” approach which isn’t generally a very good idea, unless your sex life is pretty radical. For most people, risk of gonorrhea, syphilis, or hepatitis B or C is very low. Unless you’re at risk for specific reasons, a positive test result for one of those infections is likely to be a false positive unless it’s confirmed by a second test. This is also true of HIV – however confirmation for HIV is routine, since it’s such a serious diagnosis. If your GP is routinely testing you for everything, you can start requesting just specific tests. The Melbourne Sexual Health Centre has a web service that lets you check what tests are recommend for someone with your risk profile. If you feel better being tested for everything, that’s fine too – just be aware that you may get a false positive or two, so don’t hit the roof the first time it happens.

Usual disclaimers attach to this post: I am not a doctor, and I am not telling you whether you should or shouldn’t have any particular test. I am suggesting you have a discussion, and make an informed decision about each individual test you’re offered.


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