cancer screening Flashcards
what is screening
tests done among people who are apparently well to identify those at an increased risk of a disease or a disorder
is screening diagnostic
no
WHO’s 10 screening principles
- Condition should be an important health risk
- natural history should be understood
- recognisable early stage
- must be beneficial to treat it early
- needs to be a suitable test
- acceptable test
- need adequate facilities for diagnosis and treatment
- repeat screening at interval for disease of insidious onset
- physical and psych harm should be less than the benefit of detection
- balance costs against benefits
how do you calculate % of patients with the disease that test postiive
sensitivity = Test Pos / (Test Pos + False Negative)
how do you calculate the % of patients without the disease that test negative
specificity = Test neg / (Test neg + false pos)
how do you calculate the % of patients with positive tests that actually have the disease?
positive predictive value of a positive test result (PPV) = Test Pos / (Test pos + False pos)
how do you calculate percentage of patients with negative test who do not have disease
Negative predictive value of a negative test result (NPV) = Test N / (Test N + False N)
how to calculate prevalence
disease present / total population
8 features for the ideal screening test
- simple
- cheap
- easily repeatable
- easy and unambiguous to interpret
- no false pos
- no false neg
- acceptable
- benefits outweigh the harms
5 additional factors for successful screening programmes
- training
- education
- mass awareness
- quality assurance
- finances
downside to screening (6)
- person is labelled as increased risk of cancer
- psychological impact
- impact of turnaround times
- successes depends on uptake
- impact of social media
- financial considerations for people attending screening
what is the only technique which has been shown to reduce breast cancer mortality in the population?
mammographic screening
facts: NHS breast screening programme (3)
- for women 50 and over
- includes a fully funded training programme
- mammograms are double read
what does an abnormal mammogram pick up?
lumps, calcification including micro calcification
stats for two-view mammography
42% more small invasive cancers detected, 3% more in situ cancers detected
what happens after an abnormal mammography
biopsy for a diagnosis, MDT (multi-disciplinary team) discussion for correlations
Facts: Cervical screening programme (4)
- method of treating early abnormalities which could lead to invasive cancer
- 1st stage is HPV primary screening and liquid based cytology
- sample of cells is taken from the cervix for analysis
- early detection and treatment can prevent 75% of cancers developing
when do you start cervical screening
25yrs - every 3 years until 49 and then every 5 years until 64
as of Jan 2020 what is now the 1st test on a cervical screening sample
high risk HPV testing, then its cytology triage
Primary HPV screening
uses HR-HPV (high risk HPV) testing as the 1st test, cytology becomes the triage test - only used when HR-HPV is found. 1 report issued with all the results
what is dyskaryosis
the changes in a cervical cell
out of the women screened annually what % have moderate or severe dyskaryosis?
0.7%
what do the majority (70-90%) of bowel cancers develop from
benign adenomatous polyps lining the bowel wall
what happens after an abnormal HPV triage
LBC, if that is also abnormal then a biopsy for diagnosis
what is the sequence in which a benign polyp develops into bowel cancer
the adenoma-adenocarcinoma sequence - it takes 10 years
aims of bowel cancer screening (3)
- detect bowel cancer at an early stage when treatments is more effective
- look for occult blood in stool
- detect polyps
when is bowel cancer screening offered
every 2 years to people aged 60-74, there’s also a one off test called bowel scope screening which is at 55
what is the FIT test
Faecal Immunochemical test
what does the FIT test do
uses antibodies that recognise human haemoglobin
Advantages of FIT test
- detects only human blood
- associated with higher programme uptake
- objective numerical result
- 1 sample required
- more sensitive than gFOB
gFOB as a test for bowel cancer compared to FIT
recognises haem component of any haemoglobin: tests for pseudo-peroxidase activity
what is the gFOB test
guaiac test which the participant smears small samples of stool from 3 different bowel movements onto the FOB test card
why are 3 bowel movements needed for the gFOB test
bowel cancer bleeds intermittently
Bowel scope screening
thin, flexible tube with a camera is used to look inside bowel (flexible sigmoidoscopy)
what happens after an abnormal FIT test
colonoscopy and biopsy interpretation, double contrast barium enema
PSA test for prostate cancer
- organ specific
- product of prostatic epithelium
- minute amounts found in serum
- normal range 0-4ng/ml
what does PSA stand for
prostate specific antigen
how useful is raised PSA
for cancer: 80% of those w cancer have raised PSA, shows tumours of large vol and that are well differentiated
for benign prostatic hyperplasia: 25-30% of men with BPH have raised PSA
how useful is low PSA
20-40% of patients with organ-confined prostate cancer have a low PSA
