Chapter 078. Prevention and Early Detection of Cancer (Part 9)

Breast CancerBreast self-examination, clinical breast examination by a care giver, and mammography have been advocated as useful screening tools. Only screening mammography alone and screening mammography with clinical examination have been evaluated in randomized controlled trials. MRI is being assessed and is more accurate than mammography in women at high risk due to genetic predisposition or in women with very dense breast tissue.A number of trials have suggested that annual or biennial screening with mammography or mammography plus clinical breast examination in normal-risk women over the age of 50 decreases breast cancer mortality. Each trial has been criticized for...
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Chapter 078. Prevention and Early Detection of Cancer (Part 9) Chapter 078. Prevention and Early Detection of Cancer (Part 9) Breast Cancer Breast self-examination, clinical breast examination by a care giver, andmammography have been advocated as useful screening tools. Only screeningmammography alone and screening mammography with clinical examination havebeen evaluated in randomized controlled trials. MRI is being assessed and is moreaccurate than mammography in women at high risk due to genetic predispositionor in women with very dense breast tissue. A number of trials have suggested that annual or biennial screening withmammography or mammography plus clinical breast examination in normal-riskwomen over the age of 50 decreases breast cancer mortality. Each trial has beencriticized for design flaws. In most trials, breast cancer mortality rate is decreasedby 20–30%. Experts disagree on whether average-risk women age 40–49 shouldreceive regular screening (Table 78-3). The significance of the screening effect inwomen aged 40–49 depends on the statistical test used. An analysis of eight largerandomized trials showed no benefit from mammography screening for womenaged 40–49 when assessed 5–7 years after trial entry. However, a small benefitemerged 10–12 years after study entry. What proportion of this benefit is due toscreening after these women turned 50 is not known. In randomized screeningstudies of women aged 50–69, the mortality decline begins about 5 years afterinitiation of screening. Nearly half of women aged 40–49 screened annually willhave false-positive mammograms necessitating further evaluation, often includingbiopsy. The risk of false-positive testing should be discussed with the patient. No study of breast self-examination has shown it to decrease mortality;however, it is recommended as prudent by many organizations. A substantialfraction of breast cancers are first detected by patients. Self-examination leads toincreased biopsy rate without reducing breast cancer mortality. Genetic screening for BRCA1 and BRCA2 mutations and other markers ofbreast cancer risk has identified a group of women at high risk for breast cancer.Unfortunately when to begin and the optimal frequency of screening have not beendefined. Mammography is less sensitive at detecting breast cancers in womencarrying BRCA1 and -2 mutations, possibly because such cancers occur in youngerwomen, in whom mammography is known to be less sensitive. MRI screeningmay be more effective. Cervical Cancer Screening with Papanicolaou smears decreases cervical cancer mortality.The cervical cancer mortality rate has fallen substantially since the widespread useof the Pap smear. Most screening guidelines recommend regular Pap testing for allwomen who are or have been sexually active for 3 years or have reached the ageof 21. With the onset of sexual activity comes the risk of sexual transmission ofHPV, the most common etiologic factor for cervical cancer. The recommendedinterval for Pap screening varies from 1–3 years. At age 30, women who have hadthree normal test results in a row may get screened every 2–3 years. An upper agelimit at which screening ceases to be effective is not known, but women ≥70 yearswith no abnormal results in the previous 10 years may choose to stop screening. Colorectal Cancer Fecal occult blood testing (FOBT), digital rectal examination (DRE), rigidand flexible sigmoidoscopy, radiographic barium contrast studies, andcolonoscopy have been considered for colorectal cancer screening. Annual FOBTcould reduce colorectal cancer mortality by a third. The sensitivity for fecal occultblood is increased if specimens are re-hydrated before testing, but at the cost oflower specificity. The false-positive rate for rehydrated FOBT is high; 1–5% ofpersons tested have a positive test. Only 2–10% of those with occult blood in thestool have cancer and 20–30% have adenomas. The high false-positive rate ofFOBT dramatically increases the number of colonoscopies performed. Two case-control studies suggest that regular screening of those >50 yearswith sigmoidoscopy decreases mortality. This type of study is prone to selectionbiases. A quarter to a third of polyps can be discovered with the rigidsigmoidoscope; half are found with a 35-cm flexible scope and two-thirds to three-quarters are found with a 60-cm scope. Diagnosis of adenomatous polyps bysigmoidoscopy should lead to evaluation of the entire colon with colonoscopyand/or barium enema. The most efficient interval for screening sigmoidoscopy isunknown, but 5 years is often recommended. Case-control studies suggest thatintervals of up to 15 years may confer benefit. One-time colonoscopy detects ~25% more advanced lesions (polyps > 10mm, villous adenomas, adenomatous polyps with high-grade dysplasia, invasivecancer) than one-time FOBT with sigmoidoscopy. Colonoscopy is well suited toscreening subjects at high risk, such as those with ulcerative colitis or familypredisposition. Perforation rates are 3/1000 for colonoscopy and 1/1000 forsigmoidoscopy. Debate continues on whether colonoscopy is too expensive andinvasive for widespread use as a screening tool in standard-risk populations. DREand barium enema are both insensitive as screening tools.