Sometimes statistics are  like a sly old fox. They can be used malevolently to persuade members of the public about things they don’t know much about.

The pros and cons of breast cancer screening is in the news yet again today.

Probably every woman should look into this in depth but to help you first before you do, it is necessary to know the meaning of the Number Needed to Treat (NNT). Unless this is understood, people with a vested interest might run rings round you and you won’t know what to believe or worse still will believe the wrong thing.

Here is a brief account of NNT

COUNTRY: UK

This problem – and major problem it is – of not knowing who will benefit, and for that matter who will be harmed also lies at the heart of the screening debate, which has once again been re-ignited by a ‘new’ report on the benefits and harms of breast cancer screening, ‘new’ being qualified because, though the report is new, the data it is based on is old. The arguments for and against screening symptom free women of a certain age for breast cancer have gone up and down like a tired see-saw for decades.

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Wandering around the internet for healthcare information can be like wandering around a wilderness.

In fact wandering about medicine itself can be wandering about a wilderness too. Fashions change. What was good advice five years ago might be completely reversed. It is no wonder that patients (and doctors too) can get confused.

Self examination of the breast to detect early abnormalities used to be advised, but no longer.

Routine examination (palpation) by a medical professional is no longer advised either.

At the moment, the advice is to be “breast aware”

The current advice in the form of a Cochrane Review can be downloaded from the link below.

REGULAR SELF EXAMINATION OR CLINICAL EXAMINATION FOR EARLY DETECTION OF BREAST CANCER

COUNTRY : DENMARK

AUTHORS’ CONCLUSIONS

Implications for practice
Data from two large trials do not suggest a beneficial effect of screening by breast self-examination whereas there is evidence for harms. One large trial investigating a combination of screening by clinical examination combined with instructions in the technique of breast self-examination was due to poor compliance. At present, screening by breast self-examination or physical examination cannot be recommended.

Implications for research
It is unlikely that additional trials investigating breast self-exami- nation as a single general screening method would be worthwhile.

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Last updated 10 March 2011
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It seems sensible that women invited to attend for breast screening mammography take up the offer. You would imagine it would benefit not only themselves but their families and those close to them too and seems the sort of responsible thing all the neighbours and work colleagues would do also. Consequently it would be easy for the woman who did not attend to be regarded as being neglectful of herself or alternatively that she was a bit disorganised. She might be made to feel guilty.

After all, the sooner breast cancer is detected, the easier it is to treat.

Oh, it was that easy!

There is a lot of controversy around the benefits and harms of breast screening and it is likely it will remain a controversial issue for some time yet.

There is a Cochrane review on mammography. The link below links to a brief extract:

SCREENING FOR BREAST CANCER WITH MAMMOGRAPHY – BRIEF ABSTRACT

COUNTRY : DENMARK

“Screening for breast cancer with mammography

Screening with mammography uses X-ray to try to find breast cancer before a lump can be felt. The goal is to treat cancer early, when a cure is more likely. The review includes seven trials that involved 600,000 women who were randomly assigned to receive screening mammograms or not. The review found that screening for breast cancer likely reduces breast cancer mortality, but the magnitude of the effect is uncertain. Screening will also result in some women getting a cancer diagnosis even though their cancer would not have led to death or sickness. Currently, it is not possible to tell which women these are, and they are therefore likely to have breasts or lumps removed and to receive radiotherapy unnecessarily. The review estimated that screening leads to a reduction in breast cancer mortality of 15% and to 30% overdiagnosis and overtreatment. This means that for every 2000 women invited for screening throughout 10 years, one will have her life prolonged. In addition, 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false positive findings.

It is thus not clear whether screening does more good than harm. Women invited to screening should be fully informed of both the benefits and harms. To help ensure that the requirements for informed consent for women contemplating whether or not to attend a screening program can be met, we have written an evidence-based leaflet for lay people that is available in several languages on www.cochrane.dk.”

The link below is to more comprehensive information produced as a Cochrane Review. It can be downloaded as a PDF:

SCREENING FOR BREAST CANCER WITH MAMMOGRAPHY -A REVIEW

COUNTRY : DENMARK

“Eight eligible trials were identified. We excluded a biased trial and included 600,000 women in the analyses. Three trials with adequate randomisation did not show a significant reduction in breast cancer mortality at 13 years (relative risk (RR) 0.90, 95% confidence interval (CI) 0.79 to 1.02); four trials with suboptimal randomisation showed a significant reduction in breast cancer mortality with an RR of 0.75 (95% CI 0.67 to 0.83). The RR for all seven trials combined was 0.81 (95% CI 0.74 to 0.87).

We found that breast cancer mortality was an unreliable outcome that was biased in favour of screening, mainly because of differential misclassification of cause of death. The trials with adequate randomisation did not find an effect of screening on cancer mortality, including breast cancer, after 10 years (RR 1.02, 95% CI 0.95 to 1.10) or on all-cause mortality after 13 years (RR 0.99, 95% CI 0.95 to 1.03).

Numbers of lumpectomies and mastectomies were significantly larger in the screened groups (RR 1.31, 95% CI 1.22 to 1.42) for the two adequately randomised trials that measured this outcome; the use of radiotherapy was similarly increased.

This leaflet on the link below raises important questions and is intended to help women decide whether or not to have routine mammography.

INFORMATION LEAFLET – SCREENING FOR BREAST CANCER WITH MAMMOGRAPHY

COUNTRY : DENMARK

What are the benefits and harms of attending a screening programme?

How many will benefit from being screened, and how many will be harmed?

What is the scientific evidence for this?

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Last updated 9 March 2011
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