lecture 9 - cancer screening Flashcards
What is the difference between screening programmes and opportunistic screening?
Screening programmes are organised activities with quality control measures to capture the whole population, while opportunistic screening is only offered when there is the chance to do so (often at the GP)
What are the 3 cancers that currently have NZ cancer screening policies?
Cervical, Breast screening, colorectal
How is cervical cancer currently screened for in NZ?
With HPV swab testing
What is the criteria for a suitable screening programme?
suitable test, effective treatment available for condition, evidence of reduced morbidity/mortality, benefit outweighs harm, healthcare system can afford follow up, cost-benefit
What is the sensitivity of a screening test?
The proportion of people who have the disease who test positive
What is the specificity of a screening test?
The proportion of people who don’t have a disease who test negative
What is the positive predictive value?
The probability that person with a positive test is true positive
What is the negative predictive value?
The probability that a person with a negative test does not have the disease
What are some of the disadvantages of screening?
longer morbidity for those with unaltered prognosis, overtreatment, anxiety, false reassurance/false stress, unnecessary intervention, resource intensity
What is lead time bias in screening evaluation?
When screening advances the date of diagnosis of a disease and thereby extends the interval between diagnosis and death, even if the time of death is unchanged - gives a false picture that the screening has improved survival time
What is length bias in cancer screening evaluation ?
When faster growing, more deadly tumours are less likely to be picked up than slow growing tumours because of the long intervals between screening. Thus, more cancers with a good prognosis are picked up and so screening seems to be effective in improving prognosis.
How does selection bias impact the evaluation of screening?
People who accept the offer of screening may differ in the underlying risk of disease so their prognosis may be different to those who are not screened, altering the perception of the efficacy of the screening programme
What is the only study design that can effectively evaluate screening without bias?
A randomised controlled trial, with MORTALITY as the outcome
Who is eligible for cervical HPV screening?
Those aged 25-69 who have ever had intimate skin-to-skin or sexual contact every 5 years
Who is eligible for breast cancer screening?
Women aged 45-69, every 2 years
