Lecture 23 Cancer screening Cancer s deadliest weapon is its ability to metastasize What is screening It s a systematic search for cancer before any symptoms are evident Targets general population who have NO symptoms Goal is to increase odds of early detection of cancer or pre cancerous condition Main goal is to identify a treatable cancer early when it can be treated and decrease Early detection increases 5 year survival rates cancer specific mortality Pap smears is the screening technique that has saved most lives There is no benefit to screening if there s no adequate treatment Can help find cancer at an early stage When abnormal tissue cancer is found early it may be easier to treat or cure Why screen Pitfalls of screening False negatives failing to identify existing treatable cancer People who are screened often die of cancer Screening catches slow growing cancers in detectable preclinical phase Screening in aggressive cancers not as effective because if it s once every couple years the aggressive cancer might grow too big before the next screening False positives false alarms incorrectly identifying a potential cancer 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 results in symptoms or deaths also unnecessary side effects or deaths associated with treatment Labeled as having cancer has negative effects on employment and insurance options Potential health risks associated with screening techniques can affect all Ex some procedures can cause bleeding colon cancer screening can cause tears in the lining of colon x rays can cause other cancers 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 life Overdiagnosis bias screening more likely to detect slow growing tumors that might never cause symptoms or deaths This inflates 5 year survival rates for a particular screening protocol as well The ideal screen Would never have false positive results determine a person has cancer when he or she Would never have false negative results miss the cancer in a person that actually has does not cancer Doesn t exist Sensitivity and specificity Sensitivity of people with a given cancer accurately identified during screening not sensitive increased false negatives Specificity of people without cancer that are correctly identified as being cancer free not specific increased false positives Types of tests Physical exam and history examination of your body to check signs of health signs of disease such as lumps anything that seems unusual 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 test that are non invasive or surgically based Imaging techniques Magnetic Resonance Imaging MRI uses magnets to energize electrons Release of energy image Conventional x ray Ameloblastoma Computer Tomography CAT scan uses multiple high resolution x rays to generate a composite image Ultrasound uses sound waves non radiation based Positron emission tomography PET processes in the body A medical imaging technique that produces a 3 D image or picture of metabolic Detects gamma rays emitted by a radioactive tracer which is introduced into the body on a biologically active molecule 3D images of tracer concentration within the body are constructed by computer analysis The active molecule chosen for PET is a glucose analogue High concentration of tracer will identify spots of active growth tumor development Using this tracer explores the possibility of cancer metastasis Early detection beneficial Some cancers never cause symptoms or become life threatening but if found by screening test is may be treated There is no way to know if treating the cancer would help the person live longer than if no treatment was given Treatments for cancer have side effects Some cancers finding and treating the cancer early doesn t improve the chance of a cure or help the person live longer
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