Screening

Question 1

Warning

Answer 1

• Personal experience
  
  • People close to us who have/had diseases where the outcome may have been better with screening
  • Personal experience of screening
• Cultural and political dimension
  
  • Not based solely on evidence
    
    • US: periodic (annual health check)
    • UK: Long periods without any contact with health services

Question 2

Definition

Answer 2

• The presumptive identification of unrecognised disease or defect by the application of tests, examinations, or other procedures which can be applied rapidly. Screening tests sort out apparently well persons who probably have a disease from those who probably do not. A screening test is not intended to be diagnostic. Persons with positive or suspicious findings must be referred to their physicians for diagnosis and necessary treatment’

Question 3

What are screening programmes

Answer 3

• Screening is never just a test
• Screening programmes
  
  • Need a coordinated response to the results of a test
    
    • Diagnosis
    • Treatment
  • Cost-effective
  • Continuous

Question 4

WHO (Wilson and Junger) criteria (1968)

Answer 4

• The condition should be an important health problem
• There should be a treatment for the condition
• Facilities for diagnosis and treatment should be available
• There should be a latent stage of the disease
• There should be a test or examination for the condition
• The test should be acceptable to the population
• The natural history of the disease should be adequately understood
• There should be an agreed policy on whom to treat
• The total cost of finding a case should be economically balanced in relation to medical expenditure as a whole
• Case-finding should be a continuous process, not just a once and for all project

Question 5

Why do we screen

Answer 5

• Primary purpose of screening is to reduce risk
  
  • Reduce the risk of developing a disease
  • Reduce the risk of disease progression
  • Reduce the risk of death
  • Reduce the risk of an unwanted outcome (e.g. antenatal screening)
• Very occasionally, screen merely for information
  
  • E.g. Screening for Down’s Syndrome where a couple have decided that, no matter what the result is, they will carry on with the pregnancy

Question 6

Considerations before introducing a screening programme

Answer 6

• Perfect screening test
  
  • Always right
  • Non-invasive
  • Not unpleasant
  • The disease would have a cure that was always successful and with no side effects
• Have to weigh benefits and risk
  
  • Risk of harm with all screening interventions

Question 7

Considerations- an example

Answer 7

• A disease affects 1% of the population (n= 1000)
  
  • It is fatal
  • There is no treatment
  • The test for this disease is 90% accurate
• If you screened this population for the disease, how many people will test positive

Question 8

Positive or Negative- true or false

Answer 8

Question 9

Sensitivity

Answer 9

• The proportion of sick people who are correctly identified as having the condition
• Sensitivity = True positives / All persons in population with a disease
• Usually expressed as a percentage

Question 10

Specificity

Answer 10

• The proportion of healthy people who are correctly identified as not having the condition
• Specificity = True negatives/ All persons in the population without disease
• Usually expressed as a percentage

Question 11

Sensitivity and specificity- worked example

Answer 11

Question 12

Screening for motor neurone disease (MND)

Answer 12

• Imagine you are the secretary of state for health
• You are approached by a team from a world-leading university who demonstrate to you that they have developed a 100% accurate test for MND
• They recommend that the population of England should be screened for MND
• What would your response be and why

Question 13

Lead-time bias

Answer 13

Question 14

Prostate cancer

Answer 14

• Most common cancer in men in UK
  
  • 47,740 new cases per year (2014-16 average)
  • 84% survival rate at 10 years
• Usually develops slowly and asymptomatically
  
  • First signs often when prostate has enlarged to such a degree that it affects urinary flow
• Difficult to distinguish between malignant and benign enlargements of prostate (BPH)

Question 15

Prostate-specific antigen (PSA) test

Answer 15

• Developed by Richard Albin
• Designed to see if men with prostate cancer were responding to treatment
• However, also the case that the higher the PSA level, the more likely there is a cancer present
• 1986 FDA approved PSA for use in patients suspected of having prostate cancer
• Started to be used as a screening test in men who were well and had no symptoms
  
  • By mid-1990s, several million PSA tests were being performed each year

Question 16

PSA test: Evidence

Answer 16

• PLCO (Prostate, Lung, Colorectal and Ovarian) Cancer Screening Study
  
  • n= 80,000
    
    • Randomised to intervention (PSA testing over 6 years) or control (usual care)
  • the rate of death from prostate cancer was very low and did not differ significantly between the two study groups

Question 17

Why doesn’t the PSA test reduce mortality

Answer 17

• The higher the PSA level, the more likely there is cancer present BUY
  
  • PSA can be raised in infection or benign prostatic enlargement
  • Some cancers will not lead to increased PSA levels
  • 2 out of 3 men with an increased PSA will not have cancer

Question 18

Why doesn’t the PSA test reduce mortality

Answer 18

• Some cancers which lead to an increased PSA level will be very slow-growing and may never cause any problems
• Very poor indicator of cancer for 2 primary reasons
  
  • 1) Lots of false positives
    
    • Patients endure unnecessary, invasive biopsies
  • 2) Where true positive identified
    
    • Many patients would never develop the deadly form of the disease

Question 19

Overtreatment as a result of PSA test

Answer 19

• Treatment for prostate cancer is frequently radical
  
  • Radiotherapy
  • Surgery
  • Chemotherapy
• Potential side effects of these interventions include
  
  • Pain
  • Incontinence
  • ED
• Only 16% of US prostate cancer patients die from the disease

Question 20

PSA- a public health disaster

Answer 20

• No difference in outcomes between radical prostatectomy, radiotherapy, active monitoring or watchful waiting
• PSA test
  
  • PSA testing can’t detect prostate cancer and, more important, it can’t distinguish between the two types of prostate cancer- the one that will kill you and the one that won’t

Question 21

Breast cancer

Answer 21

• 55,213 cases in the UK (360 in men)
• Prognosis
  
  • Very much dependent on the type of cancer and how early the cancer is diagnosed
  • Significant improvements in survival rates over the last 20 years
    
    • May be due to screening but may also be due to better treatment or lifestyle changes

Question 22

Breast self-examination

Answer 22

• Women in the UK instructed to be breast aware
  
  • Should know how their breast usually feel
  • Assumes women will spot changes and that the identification of any changes will lead to earlier identification of breast cancer

Question 23

Breast mammography

Answer 23

• X-rays of each breast
• NHS breast screening programme
• Women aged 50-70 screened
  
  • Will be extended to cover women aged (47-73)
  • Attend for mammogram every 3 years

Question 24

Size of the tumour at the time of diagnosis before and after the introduction of mammography

Answer 24

Question 25

Breast mammography: risk v benefit

Answer 25

* Welch and Passow * If 1000 women aged 50 years are screened annually for a decade * 0.3 to 3.2 will avoid a breast cancer death * 3-14 will be overdiagnosed and treated needlessly * 490-670 will have at least 1 false alarm * Gotzsche * If 1000 women invited for screening throughout 10 years * 0.5 will avoid dying of breast cancer * 5 healthy women will be treated unnecessarily * More than 100 women will experience important psychological distress including anxiety and uncertainty for years because of false-positive findings

Question 26

Lung cancer- targetting of low-dose CT screening

Answer 26

* 26,604 participants * 55-74 years old * Minimum of 30 pack-years of smoking * Max 15 years since quitting * Divided into quintiles according to risk * Quintile 1 (lowest risk)- 0.15-0.55% risk of lung cancer * 2= 0.56-0.85% * 3= 0.85-1.23% * 4= 1.24-2% * 5= \>2%

Question 27

Positive screening results

Answer 27

Question 28

The number needed to screen

Answer 28

Question 29

Lu-Ca deaths prevented by low dose CT

Answer 29

Question 30

Summary

Answer 30

* Screening distinguishes apparently well persons who probably have a disease from those who probably do not. **A screening test is not intended to be diagnostic** * Decisions relating to screening are often not based on robust evidence * ALL screening tests have harms that need to be considered alongside any potential benefits * Pharmacies are already involved in screening and this involvement seems likely to increase in the future