Oncology Screening 4 (cancer screening)

Question 1

What is sensitivity?

Answer 1

¡The ability to detect a true positive (sensitivity)

Question 2

What is specificity?

Answer 2

¡Reject a true negative (specificity)

Question 3

What are screening principles?

Answer 3

Screening principles

• The disease
  
  • Recognisable early stage
  • Treatment available at an early stage
  • Sufficiently common in the target population
• The test
  
  • Sensitive and specific
  • Safe and acceptable
  • Inexpensive
• The programme
  
  • Adequate facilities for diagnosis
  • The benefit must outweigh physical/psychological harm
  • The benefit must justify financial cost

Question 4

What is lead-time bias?

Answer 4

• Lead-time bias
  
  • Screening detects earlier (pre-symptomatic) individuals
  • In comparison to symptomatic individuals, survival can appear prolonged
  • Even though treatment does not change
  • Due to length of time between diagnosis and death increasing

Question 5

What is length-time bias?

Answer 5

Length-time bias

• Screening detects more indolent disease
• So the compared to the non-screened population
• Same amount of aggressive tumours
• But improved survival through the pick of indolent tumours
• Which would have been picked up at a later date when symptoms arise

Question 6

What are the types of screening bias?

Answer 6

• Lead-time bias
• Length-time bias

Question 7

Who is breast cancer screening for?

Answer 7

• Women aged 50-71
• Regular (annual or 2 yearly) mammograms
• Largest mortality reduction benefit is for this age group
• Exact benefit varies by trial
• UK review suggests 20% relative breast cancer mortality reduction for women aged 50-70
• Limited evidence for women aged 40-49
• Even less for 40-44
• For 40-49 and 70-74 can be done
  
  • evidence less clear
• No evidence to suggest that having a breast implant make detecting recurrence more difficult
• With breast implant increase risk of anaplastic large cell lymphoma

Question 8

Explain colorectal cancer screening

Answer 8

• Men and women aged 60-74
• FOB testing every 2 years
• If positive, required to do 2 further tests
• Definite positives are offered colonoscopy
• One off flexi-sig is offered at 55
• Colonoscopy has a higher sensitivity and specificity (as looks at the whole colon)
• Mortality rate from colonoscopy? 1 in a….. (due to perforation as their bowels are weaker)
• 1000
• Flexible sigmoidoscopy every 5-10 years in those who refuse colonoscopy, with yearly faecal occult blood test
• Capsule colonoscopy is not recommended for screening
• Optimal testing frequency is every year and no later than every three years
• FOB (faecal occult blood) vs FIT (Faecal immunochemical testing)
• Both can be used
• FOB 3 samples on 3 different days
• FIT is one sample on one day
• FIT is superior to faecal occult blood tests
• FAP (familial adenomatous polyposis) or HNPCC (Lynch syndrome), what is it?
• Surveillance colonoscopy every 1-3 years