Lecture 16 - Cancer Screening and Prevention

Question 1

What is screening?

Answer 1

• the investigation of asymptomatic people in order to classify them as likely or unlikely t the disease
• people who appear likely to have the disease are investigated further to arrive at a final diagnosis
• those found to have the disease are treated

Question 2

What are the necessary prerequisites for screening?-

Answer 2

• suitable disease, suitable test, inexpensive, valid, possible to administer,
• important public health problem, accepted treatment for the disease, facilities for diagnosis and treatment, recognised resumptomatic of latent phase
• suitable test or examination
• acceptable to target population
• natural history of the disease should be understood
• case-funding should be continuous and not a one-off project

Question 3

What are the characteristics of diseases suitable for screening?

Answer 3

• disease should be relatively common and have severe consequences
• dosage must pass through a preclinical phase during which it is undiagnosable
• early treatment must offer some advantage over later treatment
• screening should have evidence of net benefit

Question 4

What is lead time bias?

Answer 4

• successful screening will detect disease in its preclinical phase
• the period between detention and death could therefore be longer simply because we have observed the process for longer without actually increasing the length of time between detected and onset of symptoms
• this must be accounted for when comparing survival between those screened and unscreened

Question 5

What is length time bias?

Answer 5

• reflects the fact that disease which lend themselves to be identified by screening are more likely to be insolvent and less aggressive conditions
• more aggressive disease is less likely to be detected by screening because it is likely to develop dully between uvessive routine screening points
• survival following screen detected disease may be lengthened by the relatively less aggressive nature of the disease process
• length bias may be identified by comparing the aggrsssiveness of the disease detected clinically between screens with that detected by screening

Question 6

Describe the table with a, b, c, d for positive and negative test results

Answer 6

see lecture

Question 7

Define sensitivity

Answer 7

proportion with condition who test positive

Question 8

Define specificity

Answer 8

proportion without condition who test negative

Question 9

Define postive predictive value

Answer 9

proportion with positive test who have the condition

Question 10

Define negative predictive value

Answer 10

proportion with negative test who do not have the condition

Question 11

What are the 3 major cancer screening programmes in England

Answer 11

• breast cancer
• cervical cancer
• bowel cancer

Question 12

What is the sensitivity and specificity of mammography

Answer 12

Sensitivity = women over 50, 68-90% with most trial and programmes achieving about 85%, lower in younger women
Specificity = 82-97%
Positive predictive value = 6-8% for first screens and increases for subsequent screens. Anomalies picked up initially that will be ignored in subsequent screens

Question 13

Describe the aspects the NHSBSP

Answer 13

• every 3 years for women over 50
• women over 70 have to request an appointment
• pilot work extending screening wider age range
• saves around 1300 lives each year
• for every 400 women screened regularly by NHSBSP over a 10 year period, one women fewer will die from BC than would have died without screening
• WHO estimated 30% reduction in mortality for women screened
• established in 1988
• 85 clinics across the uk
• £50 per woman screened

Question 14

What are the criticism of NHSBSP?

Answer 14

• ductal carcinoma in situ increased diagnosis as condition is usually not palpable and mostly diagnosed by mammography
• DCIS accounts for 20% of screen detected cancers
• critics have concerns that identifying DCIS is over diagnosis of breast cancer, as these lesions may nee progress or threaten the women’s life
• treatment is usually wide local excision, but 30% result in mastectomy

Question 15

Debate about benefits and harms

Answer 15

see table

Question 16

What are the potential factors related to improving attendance?

Answer 16

• simple, friendly and comprehensive information provision
• out-of-hours appointments
• provision of transport
• one-to-one follow-up of non-attenders (to address anxieties and concerns)

Question 17

Is there potential for prostate cancer screening?

Answer 17

• prostate cancer is the most common cancer in men and ay cases are diagnosed when the disease is widespread and incurable
• an accurate method of detecing disease at an earlier stage when there is a better change of cure is highly desirable
• since the introduction of PSA testing, informal screening of asymptomatic men has taken place, but there are a number of ways in which population screening for porsate cancer failed to meet accepted screening cirtierai

Question 18

What are the 3 potential tests available to prostate cancer screening?

Answer 18

1. digital rectal examination
2. transrectal ultrasound
3. prostate specific antigen

Question 19

What are the problems with PSA testing?

Answer 19

• up to two thirds of men with elevated PSA levels do not have prostate cancer but will suffer anxiety, discomfort and risk of further investigations
• the PSA test is unreliable when undertaken in different laboratories
• the natural history of the disease is poorly understood and it is not currently possible to differentiate between aggressive and indolent tumours
• a substantial proportion of patients will receive unnecessary treatment, often with serious side-effects
• 15% of men with normal PSA have prostate cancer