Lecture 23 Cancer Screening Screening Like everything else is very straight forward No What is Cancer s deadliest screening What is Screening Systematic search for cancer before any symptoms are evident Targets general population who have no symptoms Goal 1 Increase odds of early detection of cancer or pre cancerous condition Most importantly the main goal is to identify a treatable cancer early when it can be treated and decrease cancer specific mortality This is a good outcome but surprisingly rare Early detection increases 5 year survival rate Screen MANY to benefit a FEW If you screen 1 000 people over a decade 10 years Maybe only 12 of these people would actually die from cancer if left to progress Screening may identify 3 of these people and ultimately prevent them from dying of cancer This may be the best outcome from many screenings a 25 30 reduction in cancer death rates 3 out of 12 lives saved from dying that particular cancer over 10 years NOTE This reduction in cancer specific mortality is the benefit of screening There is no benefit if no adequate treatment exists Why Screen Screening tests can help find cancer at an early stage before symptoms appear When abnormal tissue or cancer is found early it may be easier to treat or cure By the time symptoms appear the cancer may have grown and spread This can make the cancer harder to treat or cure It is important to remember that when your doctor suggests a screening test it does not always mean he or she thinks you have cancer Screening tests are done when you have no cancer symptoms Pitfalls of Screening False negatives failing to identify existing treatable cancer People who are screened often die or cancer Screening events have a greater chance of missing the smaller window of detectable preclinical phase in aggressive cancers False negatives failing to identify existing treatable cancer People who are screened often die of cancer False positives false alarms incorrectly identifying a potential cancer Many more than actual correct calls 5 10 asymptotic people will get a false positive Leads to follow up tests and biopsies and anxiety Over diagnosis Unnecessary treatment of true cancers that would have gone away on own or never would have resulted in symptoms or deaths Unnecessary side effects or deaths associated with treatment Labeled as having cancer Sometimes negative affects on employment and insurance options Potential health risks associated with screening techniques can affect regardless of who is helped Sometimes screening procedures can cause bleeding or other problems For example colon cancer screening with sigmoidoscopy or colonoscopy can cause tears in the lining of the colon X rays can cause other cancers It is important to know the risks of the test and whether it has been proven to decrease the chance of dying from cancer reduced cancer mortality rates Benefits and Harms of PSA Screening for Prostate Cancer 1 000 men screened 100 120 Get false positive results may cause anxiety and lead to biopsy 110 Get a prostate cancer diagnosis and of these men at least 50 will have treatment complications such as infections sexual dysfunction or bladder control issues 4 5 Die from prostate cancer 0 1 Deaths from prostate cancer is avoided Pitfalls in Using 5 year Survival Rates to Assess Screening Protocols Lead time bias Screening may detect a cancer earlier but not affect age of mortality However since diagnosis was earlier 5 year survival rates will be greater and make the screening test appear effective at prolonging rate Over diagnosis bias Screening is more likely to detect slow growing or latent tumors that might never cause symptoms or deaths or do so much later in time This inflates 5 year survival rates for a particular screening protocol as well The Ideal Screen The perfect screen Would never have any false positives determines a person has cancer when he or she actually does not Would never have any false negative results miss the cancer in a person that actually has cancer Does not exist Healthy Individuals Small percentage tests results say patient has cancer when he or she actually does not Individuals with Cancer Small percentage tests results say patient is cancer free when he or she actually has cancer Sensitivity and Specificity Sensitivity of people with a given cancer accurately identified during Not sensitive increased false negatives Specificity of people without cancer that are correctly identified as being screenings cancer free Not specific increased false positives Warning Signs Fatigue Weight loss Night sweats Blood in urine Chronic cough Loss of appetite Recurrent fever Sudden depression New persistent pain Enlarged lymph nodes Recurrent nausea or vomiting Blood in stool either visible or detectable by special tests A recent change in bowel habits constipation or diarrhea Changes in the size or color of a mole or changes in a skin ulcer that does not heal Types of Tests Physical Exam and History Examination of your body to check signs of health including signs of disease such as lumps or anything else that seems unusual A history of the patient s health habits and past illnesses and treatment will also be taken Know your body Laboratory Tests Medical procedures that test samples of tissue blood urine or other substances biomarkers in the body Imaging Procedures Procedures that make pictures of areas inside the body Genetic Tests Tests that look for certain gene mutations that are linked to some type of cancer Ideally tests that are non invasive or surgically based Imaging Techniques Magnetic Resonacne Imaging MRI Uses magnents to energize electrons release of energy image GBM Computed Tomography CT or CAT scan uses multiple high resolution x rays to generated a composite image lung cancer Ultrasound uses sound waves Conventional X ray ameloblastoma Positron Emission Tomography A medical imaging technique that produces a 3 D image or picture of metabolic processes in the body Detects gamma rays emitted by a positron emitting radionuclide radioactive tracer which is introduced into the body on a biologically active molecule cells will use in process of growing 3D images of tracer concentration within the body are constructed by computer analysis Often the active molecule chosen for PET is a glucose analogue The high concentration of tracer will identify spots of active growth tumor development Use of this tracer to explore the possibility of cancer metastasis is the most common type of
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