Breast screening: the enthusiast's view
Mr Lester Barr explains why he thinks screening is still the best weapon in the battle against breast cancer
Despite new drugs and new treatments, breast cancer remains one of the big unsolved health problems of our time. It is the major cause of death for women between 35 and 50. Every GP has personal experience of the impact it can have on family life. Every woman knows someone who has had breast cancer. There are many enthusiasts for the NHS breast screening programme throughout the UK who believe screening is an important tool in our battle against this disease.
Case for the prosecution
Arguments against the NHS breast screening programme seem to fall into two broad categories: first, that screening causes more harm than good and second that the money would be better invested in areas such as research into new treatments.
There are, of course, several well-known limitations to breast screening. It only applies to a specific age group (50-69) and uptake tends to be better in the well-heeled middle-classes. Some breast cancers are missed. Some are slow-growing borderline lesions where early diagnosis may not be important.
Some women have unnecessary biopsies of benign lesions.
But as each year goes by the claim screening fails to improve survival becomes less convincing. There are clear reductions now in breast cancer mortality among women who accept screening compared with those who do not1.
Of course, the natural history of breast cancer is long, so that a cancer prevented by screening may not translate into a survival benefit until 20 years later. And, of course, population-based breast screening mortality is harder to improve unless uptake rates are high (they currently run at around 70 per cent in the UK). Compliance tends to be lower in inner-city areas and among ethnic minority groups. But these are hardly reasons to abandon the whole programme.
A commonly quoted example of the harm that screening can do is the problem of ductal carcinoma in situ. Sceptics have claimed that this, which now accounts for 20 per cent of lesions picked up by breast screening, is overdiagnosed and overtreated. Perhaps it could be quietly left alone, and would never progress into invasive cancer? Again, as years go by, the evidence mounts that ductal carcinoma in situ is truly pre-malignant. There is a significant recurrence rate among patients in whom it is diagnosed but not adequately removed and in half of these cases the recurrence is with invasive breast cancer.
High-grade ductal carcinoma in situ produces high-grade invasive cancers. About one in four women with mammographically detected ductal carcinomas in situ have histological evidence of invasion or positive lymph nodes at the time of diagnosis.
The proposal to quietly ignore or observe it is simply no longer credible. The natural history is not benign. But the progression from atypia to ductal carcinoma in situ to invasion to metastases to death may take a long time perhaps 20 years. Ductal carcinoma in situ diagnosed by screening in the 1990s will not, therefore, translate into survival benefit until well into the next decade.
The way forward?
At first glance, the suggestion that we divert money spent on breast screening into research seems attractive. If we can find a cure there would be no need for screening. But many people, myself included, are increasingly sceptical that any 'final cure' will be found. Will yet more research into the pharmaceutical manipulation of metastatic cells be the answer?
Paradoxically, one of the conclusions that seems to be emerging from our understanding of the molecular biology of cancer is that such predictions may be wrong2. The heterogeneous nature of mutating cancer cells, the thousands of sites of corrupted data on the malignant cell's genes, the complexities of cellular mechanisms, the limitations imposed by toxicity to normal cells all may prove insurmountable problems in the search for gene therapies or drugs.
A better strategy may be to look at the other end of a cell's cancer journey diagnosis and prevention. In the short-term this will involve investing more (not less) in screening to improve methodology, uptake and quality assurance standards. The proportion of small cancers less than 15mm and less than 10mm detected by the NHS breast screening programme rises each year3. Earlier diagnosis means less treatment morbidity.
Most women have breast-conserving surgery; sentinel node biopsy rather than full clearance is ideal for screen-detected cancers; most have endocrine therapy rather than chemotherapy. We should invest more in screening younger women with a family history as evidence is growing that this group also benefits.
Investment in screening, early diagnosis and prevention may turn out to be a better bet for the future than investment in yet more drugs for metastatic cancer. This will be the focus of our research in Manchester over the next decade as we open Europe's first purpose-built breast cancer prevention centre. If you too are a screening enthusiast please look at our website (www.genesisuk.org) and offer us your support.
1 Duffy SW et al. The impact of organised mammography service screening on breast carcinoma mortality in seven Swedish counties. Cancer 2002;95:458-69
2 Barr L, Evans DG. There may never
be a final cure for breast cancer.
Eur J Surg Oncol 2001;27:338-339
3 British Association of Surgical Oncology Breast Group. An audit of screen detected breast cancers for the year of screening April 2000 to March 2001. London: BASO
· Those screened have lower breast cancer mortality
· Earlier diagnosis allows easier treatment
· Multidisciplinary screening teams improve quality of care for all
· The lower the compliance, the lower the effect on population breast cancer mortality
· Screening uptake is often low in areas of social deprivation
· Interval cancers
· Some unnecessary benign biopsies
· Some borderline lesions may do well even without screening
Early diagnosis and prevention: keys to help the next generation
prevention: keys to help
the next generation
· Improve screening methodology
· Improve screening uptake
· Offer screening to younger women at high risk
· Research into ductal carcinoma in situ to prevent progression
· Research into prevention strategies such as diet, lifestyle, endocrine modulators, breast physiology, genetics