9: Secondary Prevention & Screening Flashcards
What is secondary prevention?
Reducing the impact of a disease that has already occurred - finding hidden/unmanifested disease
What can screening pick up on?
- small size and stage cancers
- pre-invasive lesions (DCIS, CIN)
- dysplasia phase (eg CRC polyps)
What are the WHO screening principles?
- condition should be an important health risk
- natural history should be well understood
- recognizable early stage
- early treatment should be beneficial
- there should be a suitable, acceptable test
- adequate facilities for diagnosis and treatment
- repeat screening at interval for disease of insidious onset
- physical and psychological harm should be less than benefit of detection
- costs should be balanced against benefits
Ho do you measure sensitivity?
True positive / (true positive + false negative)
How do you measure specificity?
True negative / (true negative + false positive)
How do you calculate the positive predictive value of a positive test result?
PPV = TP/ (TP+FP)
What is the positive predictive value?
% of patients with a positive test that actually have the disease
How do you calculate the negative predictive value of a negative test result?
NPV = TN / (TN + FN)
When is the most effective time for screening during the natural history of cancer?
Before symptomatic presentations and metastatic spread.
Optimal if metastatic spread is also before symptoms present
What are the downsides of screening?
- labels a person as increased risk of cancer
- psychological impact
- impact of turnaround times
- success depends on uptake
- financial considerations for those attending screening
Fill in the blanks:
__-__% of bowel cancers develop from benign adenomatous ___ lining the bowel wall.
The adenoma-adenocarcinomas sequence takes approximately __ years, with up to __ years before symptoms develop.
The ___ test is used for bowel cancer screening
- 70-90%
- Polyps
- 10
- 15
- FIT
What does bowel cancer aim to detect?
What does it look for?
Aims to detect: early stage bowel cancer or polyps.
Looks for: occult blood in the stool
What cohort does bowel cancer screen and how often?
Men and women aged 60-74 every 2 years
What are the advantages of the FIT test?
- detects only human haemoglobin
- associated with higher programmed uptake
- objective numerical result (increased sensitivity)
- only one sample required
- more sensitive than gFOB
Describe bowel scope screening?
Uses a camera, sigmoidscopy.
Aged 55
From 60 onwards, you can do a home test kit instead
