BME 301.ppt

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1、BME 301,Lecture Thirteen,Review of Lecture 12,The burden of cancer Contrasts between developed/developing world How does cancer develop? Cell transformation Angiogenesis Motility Microinvasion Embolism Extravasation Why is early detection so important? Treat before cancer develops Prevention Accurac

2、y of screening/detection tests Se, Sp, PPV, NPV,Question 4: If a clinical test for a certain type of cancer is found to have a sensitivity of 100%, is there any reason to worry about the specificity?,Question 3: If a clinical test for a certain type of cancer is found to have a specificity of 100%,

3、is there any reason to worry about the sensitivity of the test?,Amniocentesis Example,Amniocentesis: Procedure to detect abnormal fetal chromosomes Efficacy: 1,000 40-year-old women given the test 28 children born with chromosomal abnormalities 32 amniocentesis test were positive, and of those 25 we

4、re truly positive Calculate: Sensitivity & Specificity PPV & NPV,Possible Test Results,Se = 25/28 = 89% Sp =965/972 = 99.3% PPV = 25/32 = 78% NPV =965/968 = 99.7%,Dependence on Prevalence,Prevalence is a disease common or rare? p = (# with disease)/total # p = (TP+FN)/(TP+FP+TN+FN) Does our test acc

5、uracy depend on p? Se/Sp do not depend on prevalence PPV/NPV are highly dependent on prevalence PPV = pSe/pSe + (1-p)(1-Sp) NPV = (1-p)Sp/(1-p)Sp + p(1-Se),Is it Hard to Screen for Rare Disease?,Amniocentesis: Procedure to detect abnormal fetal chromosomes Efficacy: 1,000 40-year-old women given the

6、 test 28 children born with chromosomal abnormalities 32 amniocentesis test were positive, and of those 25 were truly positive Calculate: Prevalence of chromosomal abnormalities,Is it Hard to Screen for Rare Disease?,Amniocentesis: Usually offered to women 35 yo Efficacy: 1,000 20-year-old women giv

7、en the test Prevalence of chromosomal abnormalities is expected to be 2.8/1000 Calculate: Sensitivity & Specificity Positive & Negative Predictive Value Suppose a 20 yo woman has a positive test. What is the likelihood that the fetus has a chromosomal abnormality?,Possible Test Results,Se = 2.5/2.8

8、= 89.3% Sp 990.2/997.2= 99.3% PPV = 2.5/9.48 = 26.3% NPV =990.2/990.5 = 99.97%,Prostate Cancer,Early Detection,Prostate gland contributes enzymes, nutrients and other secretions to semen.,http:/ Cancer: Statistics,United States: 230,110 new cases in US 29,900 deaths in US 2nd leading cause of cancer

9、 death in men Worldwide: 543,000 new cases each year Third most common cancer in men Risk Factors: Age Race (incidence 3X higher in African Americans) Family history of prostate cancer,Global Incidence of Prostate Cancer,Figure 5.45,Development of Prostate Cancer,Normal prostate: 30-50 branched glan

10、ds leading to urethra Covered by columnar epithelium Precancer of the prostate: Figure 5.50,Development of Prostate Cancer,Prostate Cancer: Slow, but continuously growing neoplasia Preclinical form develops at age 30 Remains latent for up to 20 years Can progress to aggressive, malignant cancer Peak

11、 incidence: 7th decade of life Signs and symptoms: Often asymptomatic in early stages Weak or interrupted urine flow Inability to urinate These are symptoms of prostate enlargement,Risk of Prostate Cancer in Next 5 Yrs,Normal Prostate,http:/www.prostatitis.org/1normalgland.gif,http:/ Gland,Pre-cance

12、rousGlands,http:/medlib.med.utah.edu/WebPath/jpeg1/MALE116.jpg,http:/medlib.med.utah.edu/WebPath/jpeg1/MALE138.jpg,Prostate Cancer,http:/medgen.genetics.utah.edu/photographs/diseases/thumbnails/male074_small.,Prostate Cancer,Screening (American Cancer Society recs): Annual serum PSA test beginning a

13、t age 50 Annual digital rectal exam at age 50 Treatment: Surgery, radiation therapy, hormone therapy, chemotherapy 5 year survival All stages: 98% Localized disease: 100% Distant metastases: 31%,Screening Guidelines for the Early Detection of Prostate Cancer, American Cancer Society 2003,The prostat

14、e-specific antigen (PSA) test and the digital rectal examination (DRE) should be offered annually, beginning at age 50, to men who have a life expectancy of at least 10 years. Men at high risk (African-American men and men with a strong family history of one or more first-degree relatives diagnosed

15、with prostate cancer at an early age) should begin testing at age 45. For men at average risk and high risk, information should be provided about what is known and what is uncertain about the benefits and limitations of early detection and treatment of prostate cancer so that they can make an inform

16、ed decision about testing.,Recent* Prostate-Specific Antigen (PSA) Test Prevalence (%), by Educational Attainment and Health Insurance Status, Men 50 Years and Older, US, 2001-2002,*A prostate-specific antigen (PSA) test within the past year. Note: Data from participating states and the District of

17、Columbia were aggregated to represent the United States. Source: Behavioral Risk Factor Surveillance System Public Use Data Tape (2001, 2002), National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention and Prevention, 2002, 2003.,Recent* Digital R

18、ectal Examination (DRE) Prevalence (%), by Educational Attainment and Health Insurance Status, Men 50 Years and Older, US, 2001-2002,*A digital rectal examination (DRE) within the past year. Note: Data from participating states and the District of Columbia were aggregated to represent the United Sta

19、tes. Source: Behavioral Risk Factor Surveillance System Public Use Data Tape (2001, 2002), National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention and Prevention, 2002, 2003.,What happens if DRE & PSA are +?,Biopsy of prostate ($1500) Insert ne

20、edle through wall of rectum into prostate Remove fragments of prostate Examine under microscope,http:/ for Localized Prostate Cancer,Radical prostatectomy (remove prostate) Usually curative Serious side effects: Incontinence (2-30%) Impotence (30-90%) Infertility Conservative management Just watch u

21、ntil symptoms develop,Does Early Detection Make a D?,10 Yr Survival Rates for Localized Prostate CA: Grade I: Surgery 94% Conservative Rx 93% Grade II: Surgery 87% Conservative Rx 77% Grade III: Surgery 67% Conservative Rx 45% Makes a difference only for high grade disease,Challenges of Screening,Pr

22、ostate cancer is a slow-growing cancer Not symptomatic for an average of 10 years Most men with prostate cancer die of other causes Treatment has significant side effects 50 year old man: 40% chance of developing microscopic prostate cancer 10% chance of having this cancer diagnosed 3% chance of dyi

23、ng of it,Should we screen?,Yes: Localized prostate cancer is curable Advanced prostate cancer is fatal Some studies (not RCTs) show decreased mortality in screened patients No: False-positives lead to unnecessary biopsies Over-detection of latent cancers We will detect many cancers that may never ha

24、ve produced symptoms before patients died of other causes (slow growing cancer of old age) No RCTs showing decreased mortality,Clinical Evidence,Tyrol, Austria Mortality from prostate cancer: Constant from 1970-1993 Screening with DRE & serum PSA began in 1993 Mortality decreased 42% since 1993 in T

25、yrol Mortality remained constant in other parts of Austria where screening not performed,Clinical Evidence,Three case-control studies of DRE Mixed results One completed RCT of DRE & PSA Found no difference in # of prostate cancer deaths between groups randomized to screening and usual care,Why are R

26、CTs so Important? Lead Time Bias,Survive 15 yearspost-diagnosis,Survive 25 yearspost-diagnosis,Randomized Clinical Trials Underway,Prostate Cancer vs. Intervention Trial (US) Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (US) European Randomized Study for Screening for Prostate Cance

27、r 239,000 men 10 countries Will be complete in 2008,Do All Countries Screen with PSA?,United States: Conflicting recommendations Europe: No Not enough evidence that screening reduces mortality,Conflicting Recommendations in US,Guide to Clinical Preventive Services Do NOT screen using DRE or serum PS

28、A American College of Preventive Medicine Men aged 50 or older with 10 yr life expectance should be informed and make their own decision American Cancer Society (and others) Men aged 50 or older with 10 yr life expectancy should be screened with DRE and serum PSA,USPSTF Recommendation,The USPSTF fou

29、nd: good evidence that PSA screening can detect early-stage prostate cancer but mixed and inconclusive evidence that early detection improves health outcomes. Screening is associated with important harms, including frequent false-positive results and unnecessary anxiety, biopsies and potential compl

30、ications of treatment of some cancers that may never have affected a patients health. The USPSTF concludes: that evidence is insufficient to determine whether the benefits outweigh the harms for a screened population.,Question 6: Would you take the test described in question 5 if you had a history o

31、f smoking 2 packs of cigarettes per day for the last 30 years?,Question 5: A new blood test to screen for lung cancer has a sensitivity of 99% and a specificity of 50%. If the test is positive, your physician will recommend that you have a bronchoscopy to confirm the diagnosis. Would you take the te

32、st?,PSA Test,Details,The PSA Test,What is PSA? Prostate-specific antigen A glycoprotein responsible for liquefaction of semen Highly specific for prostate (only made by the prostate) PSA test is a blood test to measure PSA levels Why measure PSA to screen for cancer? PSA levels are closely (but not

33、definitively) associated with prostate cancer May be elevated in benign conditions (BPH, Prostatitis) Not always high in cancer Cost: $30-$100,PSA Levels,Normal PSA Levels:10 ng/ml,Sensitivity and Specificity of PSA,How to determine Trial: Serum PSA Biopsy (Gold standard) If BX is positive and PSA i

34、s positive: get TP If BX is positive and PSA is negative: get FN If BX is negative and PSA is negative: get TN If BX is negative and PSA is positive: get FP BUT: if BX is negative: Did BX just fail to sample area with cancer? Hard to calculate Specificity - TN/(TN+FP) Cutpoint of 4 ng/ml Sensitivity

35、 = 63-83% Specificity = 90%,Predictive Value Calculation,Screening Performance: Se = 73%; Sp = 90% Number Tested: N=1,000,000; Prevalence = 2% Costs: Screening = $30; Follow up biopsy = $1500 What are PPV & NPV? What is screening cost? What is biopsy cost? What is cost/cancer found?,PSA Example Pred

36、ictive Value,PPV =14,600/112,600 = 13% NPV =882,000/887,400 = 99%,PSA Example Cost,Cost to Screen =$30*1,000,000+$1500*112,600 =$168,900,000 Cost/Cancer = $168,900,000/14,600=$13,623,Question 6: Would you take the test described in question 5 if you had a history of smoking 2 packs of cigarettes per

37、 day for the last 30 years?,Question 5: A new blood test to screen for lung cancer has a sensitivity of 99% and a specificity of 50%. If the test is positive, your physician will recommend that you have a bronchoscopy to confirm the diagnosis. Would you take the test?,Health Policy Space,Health,$,Wo

38、rsens Health Saves Money,Improves Health Costs Money,Improves Health Saves Money,Worsens Health Costs Money,Vaccines,Most Interventions,?,Richard J. Babaian, MD,New Technologies: Improved Screening,Additional serum markers Improve Sp Free PSA PSA density PSA velocity Predict those cancers which will

39、 progress to advanced disease Gene chips,Review of Lecture 13,Prostate cancer Leading cause of cancer in men in USA 2nd leading cause of cancer death in men in USA Slow growing cancer of old age Precancercancer sequence Precancer is very common PSA Serum antigen closely (but not exclusively) associa

40、ted with prostate cancer Should we screen with PSA? Early prostate cancer is curable No RCTs showing decreased mortality yet Screening can lead to unnecessary biopsies and over-treatment of latent cancer,Assignments Due Next Time,WA8 CPS 119-129 http:/www.bccancer.bc.ca/NR/rdonlyres/el4cwwvk5dno63vawc6b4utxl6mpmi456q7crjryhd3wrsaaemzc4myftydgn5dlwgu42ilcxu6nfc/PSAwebBrochure1.pdf,