BIO 302 - Exam 2 - Screening for Cancer PowerPoint

Question 1

Cancer patient management is guided by the following principles:

Answer 1

(1) The earlier the cancer is discovered and effectively treated, the better the outcome for most cancers.

(2) The right therapy and management are dependent on the right diagnosis and assessment.

(3) All cancer therapies have undesirable effects: the goal is to have desirable effects outweigh undesirable effects.

Question 2

Screening for cancer involves:

Answer 2

(1) Testing people without symptoms
(2) Testing defined populations (not everyone)
(3) Usually restricted to individuals at risk for cancer

Question 3

Risk is defined by what 5 things:

For most cancers there are no effective screening tests!

Answer 3

Age (in everyone)
Family history
Personal history
Genotype
Exposures

Question 4

Why Screen for Cancer?

Answer 4

(1) Cancer is a common disease
Pre-clinical phases of cancer can be long, therefore, there’s time for proactive search for early stage disease.

(2) Cancer in late stage (after symptoms develop) can be lethal and treatment of advanced cancers is NOT very effective overall - It’s dangerous to wait.

(3) Effective screening to find and treat cancers or pre-cancers at early stages of development can save lives for some cancer types (proven for cervical and colon cancer).

Question 5

What are the problems?

Answer 5

False positive tests lead to over-diagnosis, over-treatment and needless burden for patient and healthcare system

False negative tests lead to under-diagnosis and missed opportunity for life-saving early treatment

Question 6

Performance of Screening Tests:

Answer 6

Disease Present:
True Positive and False Negative

No Disease:
False Positive and True Negative

Question 7

What is Test Sensitivity?

Sensitivity = 100% if…

Sensitivity is 80% if the test is positive in 80% of patients with the disease but 20% of those with the disease would go undetected as ______ ______.

Sensitivity does not take ______ ______ into account.

Answer 7

Test sensitivity: A test’s ability to correctly identify those WITH the disease.

Sensitivity = 100% if ALL patients with disease test positive*
*Tests are never perfect – so this NEVER happens

Sensitivity is 80% if the test is positive in 80% of patients with the disease but 20% of those with the disease would go undetected as FALSE NEGATIVES

Sensitivity does not take FALSE POSITIVES into account, so some people may be falsely diagnosed even if the sensitivity is 100%

Question 8

What is Test Specificity?

Specificity = 100% if…

Specificity is 80% if the test is negative in 80% of patients without the disease but 20% of those without the disease would be misdiagnosed as ______ ______.

Specificity does not take ______ ______ into account.

Answer 8

Test specificity: A test’s ability to correctly identify those WITHOUT the disease.

Specificity = 100% if all those WITHOUT disease test negative*
*Tests are never perfect - so this NEVER happens

Specificity is 80% if the test is negative in 80% of patients without the disease but 20% of those without the disease would be misdiagnosed as FALSE POSITIVES

Specificity does not take FALSE NEGATIVES into account, so some people with disease may be falsely assured that they don’t have the disease even if the specificity is 100%

Question 9

What is the diagnostic threshold (DT)?

Answer 9

When everyone in a population is tested, those with and without disease will have a spectrum (bell curve) of results due to human variation; the curves usually overlap.

In the overlapping range, people with or without disease may have the same test rest; the more the curves overlap, the less the discriminatory power of the test.

The DT will always miss some true positives and includes some false negatives.

Question 10

moving the diagnostic threshold (DT) changes the proportion of false results (slide 11)

Question 11

What is the Positive predictive value (PPV)?

Equation?

As ______ ______ go up, the predictive value of the test declines.

Answer 11

Positive predictive value (PPV): the probability that those with a positive test actually have the disease.

PPV = _______ True Positives__________ x 100
True Positives + False Positives

false positives

Question 12

What is the Negative predictive value (NPV)?

Equation?

As ______ ______ go up, the predictive value of the test declines.

Answer 12

Negative predictive value (NPV): the probability that those with a negative test don’t have the disease.

NPV = ________True Negatives_________ x 100
True Negatives + False Negatives

false negatives

Question 13

The ______ the disease, the more likely ______ ______ are to be.

A test that is 100% ______ and 100% ______ would be needed.

Answer 13

rarer / false positives

sensitive / specific

Question 14

3 common diseases but poor test performance.

Answer 14

Mammography - Breast Cancer - 50-60% False Positives
Fecal occult blood - Colon - 90-98% False Positives
Prostate specific antigen (PSA) - Prostate - 75% False Positives.

Question 15

US Preventive Services Task Force (USPSTF) evaluation and recommendations

What separates the different grades?

Answer 15

Slide 19

Question 16

What are our most Effective Screening Tools?

Answer 16

Pap smear (cervical cancer)
Colonoscopy (colon-rectal cancer)
Low-Dose Computed Tomography (lung cancer)

Question 17

Per ______ women, ______ life is saved and ______ women are harmed (over-treated) with mammography vs. without

Answer 17

1,000 /1 / 100

Question 18

Screening that saves lives (definitively reduces deaths) from these specific cancers:

Answer 18

Cervical cancer
Colon and rectal cancer
Lung Cancer in high risk groups

Question 19

USPSTF recommends colorectal cancer screening to begin at age ______.

Answer 19

45

Question 20

When does the USPSTF recommend screening for cervical cancer in women?

Answer 20

A+

21-65 years with cytology (pap smear) every 3 years.

30-65 years combination of cytology and HPV screening every 5 years.

Question 21

What are the two kinds of bias mislead physicians into thinking screening saves lives?

Answer 21

Lead Time Bias
Early Dx and Rx doesn’t change the ultimate outcome for some cancers (we don’t have effective Rx)
A 5-year-survival would appear to improve spectacularly, but patient dies of disease at same age
Depends on the cancer biology and the available treatments

Over-Diagnosis Bias
Not all cancer is aggressive and progresses
Depends on the cancer biology irrespective of treatment
Lumping all cancers together is misleading and associated with over-treatment (breast; prostate)

Question 22

Lung cancer: Low-dose CT screening (American Cancer Society guidelines) for people who (5 things):

Answer 22

Lung cancer: Low-dose CT screening for people who:
Are current or former smokers aged 55 to 80 years
Have smoking history of at least 30 pack-years
Have no prior history of lung cancer
Willing and able to undergo curative surgery

Question 23

Take home messages: screening

Answer 23

The goal of screening is to detect disease early and treat before the cancer has progressed.

Effective screening is defined by a in decrease mortality from the cancer in the screened vs. unscreened population.

Conversely, it’s ineffective if it doesn’t decrease mortality.

The benefit-to-harm ratio of screening using a particular test depends on false negative and false positive rates.

False positives lead to over-diagnosis and over-treatment, increased medical costs and an increased patient burden

False negatives forestall potentially life-saving therapy

The utility of a screening test depends on its predictive value and the prevalence of the disease.