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Chapter 2

HSS 3332 Chapter Notes - Chapter 2: Prostate Cancer, Thyroid Cancer, Overdiagnosis

Health Sciences
Course Code
HSS 3332
Sarah Fraser

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Diagnostic Technologies
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
of 60
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
microscopic diseases
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
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