The previous chapter dealt with primary prevention — effectively, in the context of skin cancer, how can we minimise exposure to UVR in those with pale skins. Although I did not discuss it in detail, whilst a reduction in UVR exposure (and hence skin cancer) is theoretically achievable, in practice it is difficult because it involves behavioural change. Reducing UVR exposure may mean changes in clothing, sporting activities, or choice of holiday destination. It also appears to conflict with the desires or goals of many people, who want to ‘sport‘ a suntan (note the English language usage, ‘sport‘). Most high streets have tanning shops, proof that there is a clear difference in narrative between many in the population and those who claim to be ‘health experts‘.
Although objective measures of individual UVR exposure are lacking, in some parts of the world, it does seem that habits at a population level have been changed. Australia is an example, where limited interventional studies have been supportive of the idea that sun protection using sunscreens reduces dysplastic lesions and some skin cancers. Skin cancer rates in some parts of Australia are however orders of magnitude higher than in many European countries, so the magnitude of effect may be more marginal in these latter populations (such of those of the UK).
By contrast, this chapter focusses on secondary prevention, which I define as being concerned with reducing morbidity and mortality from skin cancer by diagnosing premalignant and malignant lesions earlier.
What is the point of secondary prevention?
Skin cancer management is full of apparent paradoxes. The above paragraphs provided an example. We know the major cause for skin cancer is UVR exposure, and we estimate that we might reduce the incidence of skin cancer by close to 80% if we could alter population exposure to UVR. But in practice, reducing UVR means behavioural change, and that is hard.
These apparent paradoxes are also present when we talk about secondary prevention. Skin cancers are usually visible, with all that is required for diagnosis being an expert pair of eyes. No machinery such as a MRI scanner, or colonoscope, is necessary. This would seem to make secondary prevention easier. Similarly, skin cancer is more common than the sum total of all other cancers in many populations. High incidence rates normally argue in favour of secondary prevention strategies. So why is there so little secondary prevention — why no national skin cancer screening?
Skin cancer screening: the 'problem' of the low case-fatality rate
Most skin cancers are keratinocyte cancers (usually BCCs or SCCs). Mortality from BCC is so rare as to be routinely ignored by health care systems; and the case-fatality rate of SCC is close to a few percent. Melanoma is of course different, with a case-fatality rate of approximately 20%, but melanoma affects only just over 1% of the population of the UK. This gives an overall mortality rate of close to 1:500. True, melanoma often affects younger people than many other malignancies, but still the low overall death relate from skin cancer, may make arguments in favour of population screening harder to sustain.
If the above argument holds for invasive lesions, it is even more true of dysplastic lesions such as as actinic keratoses or intraepithelial carcinomas, simply because the risk of progression to malignancy is so low.
Skin cancer screening: money, money, money
Without wishing to minimise the opprobrium that is often heaped upon economists, mortality (or morbidity) is not the only thing that matters when considering screening: money matters, too.
Although skin cancer is very common, treatment costs are often quite low in comparison with many other cancers. Surgery is normally carried out under local anaesthetic as an outpatient or office procedure (no expensive anaesthetists or ITU staff needed….). True, drugs for metastatic melanoma are expensive, but they are used in only a minority of patients. Even the clinical assessment or staging for the majority of skin cancer patients does not involve imaging or radiology. Put simply, these factors make arguments for screening based on ‘reducing health care costs’ much harder to maintain.
Skin cancer screening: a waste of time?
This subheading is meant to be provocative. Nor is it a fair summary of my argument, which is more nuanced. The case for skin cancer screening has not been convincingly made. Studies in Germany have suggested it may be worthwhile from the point of view of a single health care insurer or provider (such as the NHS), but the matter is not settled. Indeed, arguments in favour of population screening, would be much easier to make in populations with higher cancer rates such as we see in some parts of Australia or the US.
Formal versus more informal approaches
Although no country (as far as I know) has launched formal national screening programmes such as we see for cervical cancer in the UK, there seems little doubt that skin cancers are diagnosed at an earlier stage than they once were, and that this is likely to have reduced morbidity and mortality from skin cancer. I will label these approaches ‘informal‘, although this is not meant to imply that they do not work.
Why then is skin cancer diagnosed earlier than it once was?
There are a number of informal interventions at work here. Some of the more important ones are:
- Awareness of skin cancer is higher than it once was. People have higher health literacy levels than they once did, and have access to more (especially visual) information. If you look at the Breslow thickness of melanoma at presentation over the last century it has dropped dramatically.
- People access health care more than ever. This means that it is now more likely that patients may ask: ‘while I am here doctor, can you have a look at this mark on my skin….?’
- Even if patients who attend a doctor for another reason, do not ask for their skin to be checked, in many parts of the world, a whole body skin-exam is tagged on to many consultations. Even in dermatology departments, our own experience is that up to one third of melanomas we diagnose are only picked up because a whole body skin exam is offered whatever the original reason for the consultation.
- In areas of the world with very high skin cancer rates, many people routinely see a dermatologist every three to six months, just as many of us arrange to visit a dentist regularly. Premalignant lesions and malignancies will be detected and treated, on their merits, and decisions about the appropriate frequency of visits made.
Informal detection is not cost neutral
These informal mechanisms of earlier skin cancer detection seem reasonable to me (in many instances). This does not mean that they are all appropriate in all populations, nor that they do not have an opportunity cost.
For instance, many ‘awareness raising’ campaigns for skin cancer, may lower the signal:noise ratio of patients seen by dermatologists. If the supply of dermatologists is suboptimal (e.g. the UK), outcomes could conceivably be worse at a population level. At the other extreme, medical professionals may ‘generate’ unnecessary care — for instance benign nevi removal, with spurious justifications (or on the basis of inadequate clinical skills) seems to me to be almost an epidemic in some parts of the world.
The future for skin cancer screening
The main cost in screening is the ‘cost’ of the person making the clinical decision. At present this is a doctor. It is not inconceivable that non-physicians could be trained and certified to take on this role. And whereas in some countries such as the UK, access to specialists expertise is via a genealist, it is not impossible to imagine direct access reducing costs. Finally, there is little doubt that assessment of many lesions might be achieved using automated image capture, and reading of images by ‘human experts’ at a distant site or — more likely in the long term — by machines. Sadly, for the present, you have to keep learning how to do it the old fashioned way 🙁
Skincancer909 by Jonathan Rees is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Where different rights apply for any figures, this is indicated in the text.