cancer screening

Question 1

what is meant by specificity

Answer 1

the ability of a test to pick up those who are negative for a disease

Question 2

what is meant by sensitivity

Answer 2

the ability of a test to pick out those who are positive

Question 3

what is the positive predictive value?

Answer 3

the % of positive results that are true positives - the higher the better

Question 4

what is the negative predictive value

Answer 4

the % of negatives that are true negatives - the higher the better

Question 5

what does successful screening involve?

Answer 5

test should be easy, acceptable and available and able to detect pre-cancerous condition

the disease:

• should have known natural history so that those who are at risk can be selected for screening
• should be of significance - high mortality/ morbidity
• treatment available and early detection improves prognosis

programme should be cost effective

Question 6

what is meant by lead time bias?

Answer 6

screening detects tumours at an earlier stage and therefore survival time appears to be longer because diagnosed earlier.

Question 7

length time bias

Answer 7

slower growing cancers have a longer latent period and more likely detected by screening and likely to have prolonged survival regardless

Question 8

which cancers are screened on a population level?

Answer 8

breast
colorectal cancer
cervical cancer

Question 9

how is cervical cancer screened for? who is screened?

Answer 9

cervical smear test can detect CIN. abnormal smears are followed up by colposcopy

women aged 25 to 49 every 3 years
women aged 50-64 every 5 years

Question 10

how is CRC screened for?

Answer 10

faecal occult blood test

if at increased risk of CRC e.g. crohns, FAP then have yearly colonoscopy surveillance