HSS 3332 Chapter Notes - Chapter 2: Prostate Cancer, Thyroid Cancer, Overdiagnosis
This preview shows half of the first page. to view the full 2 pages of the document.
i. Primer on Lead Time, Length and Over-diagnosis Bias AND Prostate Cancer:
Screening and Early Detection: Screening Controversies.
• How are lead time bias, length bias, and over-diagnosis bias defined?
Give an example of each type of bias.
o Lead time bias suggests that the natural history of the disease is not truly
affected by screening
• Ex. a patient may be diagnosed with prostate cancer at 50 years
of age through PSA-based screening.
• He then undergoes treatment but ultimately progresses and dies
at 60 years of age through PSA-based screening
• Accordingly, the same patient without screening develops
symptomatic bony metastases at the age of 58, under-goes
treatment with androgen deprivation therapy and dies at the age
• Thus, even though he was diagnosed 8 years prior through
screening, his dead was not affected by screening or early
o Length time bias suggests that annual screening is more likely to detect
slow-growing tumors, while fast growing and potentially lethal tumors are
less likely to be detected
• Example. Argued that screening for prostate cancer does not
detect the very tumors for which it is intended
ii. Over-diagnosis and Pseudo-disease: Too Much of a “Good Thing?”
• Define pseudo-disease and give an example.
o A pseudo-disease is a disease that never produced clinically meaningful
effects; we all have identifiable abnormalities
o These problems should not worry us because they never produce
significant problems for our quality of life or life expectancy
o As diagnostic testing improves there will be a huge reservoir of psedo-
o Continual increases in the incidence and prevalence of cancer and other
o Example. Thyroid cancer; As microscopic inspection of the thyroid
improves, more adults will have abnormalities
• Study of Finnish adults: made slices at 2.5mm intervals at
autopsy; in adults of the same age, they found 36% has some
evidence of thyroid cancer
• Realized that slicing he gland at 2.5mm intervals would still
leave many tumors undetected because there would be intervals
of 2.5mm between the slices
• The method would detect tumors larger than 2.5mm but would
capture only 1/5th of the tumors 5mm in size
You're Reading a Preview
Unlock to view full version