Cancer Detection: Screening Flashcards
What proportion of people will have cancer in their lifetime?
one in three
Who does cancer impact the most?
older people- 65% of cancers in those over 65
How many cancer cases are registered a year?
around 300,000
(270000 in 2000)
What are the main cancer types diagnosed?
lung, breast, prostate and colorectal
together >50%
What is screening?
tests done to asymptomatic people to identify those at an increased risk of disease
What must be done after screening if there is a positive result?
Why is this important?
suspicion of a disease must be referred for further diagnostic testing
screening is NOT diagnostic
What are the WHO screening principles?
- Condition should be an important health risk
- Natural History should be well understood
- Recognisable early stage
- Early treatment should be beneficial
- There should be a suitable test
- The test should be acceptable to the patient
- 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
What makes up a suitable test?
- high accuracy
- high sensitivity
- high specificity
- disease with high prevalence
Describe high accuracy in a test
a certain test result must indicate a significantly higher risk of disease
cut off point must take as many diseased and as little healthy participants as possible
Define sensitivity and how to calculate it
Percentage of patients with disease who test positive
Sensitivity = True Positives / (True Positives + False Negatives)
Define:
1) a true positive
2) a false negative
3) a true negative
4) a false positive
1) someone who tests positive and who has the disease
2) someone who tests negative but has the disease
3) someone who tests negative and who is healthy
4) someone who test positive but is healthy
Define specificity and how to calculate it
Percentage of patients without the disease who test negative
Specificity = True Negatives/ (True Negatives + False Positives)
Define Positive Predictive Value (PPV) and how to calculate it
Percentage of patients with positive test who actually have disease
PPV = True Positives / (True Positives + False Positives)
Define Negative Predictive Value (NPV) and how to calculate it
Percentage of patients with negative test who do not have disease
NPV = True Negatives / (True Negatives + False Negatives)
How to calculate prevalence?
Disease present in population /Total population
Why is prevalence important in accuracy?
- rarer diseases have a higher degree of false negatives
- at the SAME sensitivity and specificity, a lower prevalence causes a lower PPV
Regarding cancer, in what situation is screening worthwhile?
when the screening detects the cancer before it is symptomatic AND before it has metastasised
What makes up the ideal screening test?
- Simple
- Cheap
- Easily repeatable
- Easy and unambiguous to interpret
- No false positives
- No false negatives
- Acceptable to the patient
- Benefits outweigh the harms
What impacts a successful screening programme?
- training and education of doctors
- training and education of the population
- mass awareness within population
- quality assurance
- finances of both organisation offering screening and individual
- social media
- turnaround times
Describe Breast Cancer Screening
- mammographic screening for all women aged 50-70 that is repeated every 3 years
- mammograms taken from two views: front and side
- mammograms double-read (by at least one consultant radiologist)
Describe what an abnormal mammogram identifies
- picks up lumps
- picks up (micro-)calcification
Describe the clinical success of two-view mammography
- 42% more small invasive cancers detected (less than 2cm)
- 3% more in situ cancers detected (especially high grade)
- ONLY technique shown to reduce breast cancer mortality in the population
What are the next steps following a positive mammogram?
- biopsy for diagnosis
- Multi-Disciplinary Team discussion for treatment plan
When was NHS cervical screening introduced?
When was the Call Recall system introduced?
1966
1988
