Cancer screening and prevention Lecture 18

Question 1

What is screening

Answer 1

Investigation of asymptomatic people in order to classify them as likely/unlikely to have the disease.
People who appear likely to have the disease are investigated further to arrive at a final diagnosis

Question 2

Prerequisities for screening

Answer 2

Prerequisites:

• Must be an important public health problem
• Must be an accepted treatment for the disease
• Suitable test acceptable for target population
• Cost should be economically balanced in relation to cost of medical care as a whole

Question 3

Diseases suitable for screening are

Answer 3

Disease should be relatively common and have severe consequences
Disease must pass through a preclinical phase bring which it is undiagnosed but detectable
Early treatment must offer some advantage over later treatment

Question 4

What is lead time bias

Answer 4

Lead Time:
Through screening as you try to pick up disease before it becomes symptomatic - may extent survival period by pulling it into asymptomatic period

• Successful screening detects disease in preclinical phase, meaning time between detection and death could therefore be longer simply because we observed it longer, rather than actually increasing lifetime of patient
• This should be accounted for when comparing survival between screened and unscreened

Question 5

What is a length bias

Answer 5

Length bias:

• Diseases identified by screening are more likely to be less aggressive conditions
• More aggressive disease is less likely to be detected by screening because it is likely to develop fully between successive routine screening points
• Hence this “increases” survival time of screened patients

Question 6

How do you decide the viability of a screening test?

Answer 6

• Calculate number of true +ve, true -ve, false +ve and false–ve’s
• Calculate sensitivity (number of +ves divided by actual number of cases)
• Specificity is proportion without condition who test negative
• Positive predictive value is proportion with positive test who have the condition

Question 7

Cancer screening programmes in England

Answer 7

Breast cancer, cervical cancer and bowel cancer (screen faeces and look for evidence of blood)

Question 8

What are the limitations for screening and what factors could improve attendance?

Answer 8

-Cost
-Travel to clinic
Potential Factors related to improving attendance
-Simple information provision
-Out-of-hours appointments
-Provision of transport
-One-to-one follow up of non-attenders to address concerns