Harrison's Internal Medicine Chapter 78. Prevention and Early Detection of Cancer
Prevention and Early Detection of Cancer: Introduction Improved understanding of carcinogenesis has allowed cancer prevention and early detection (also known as cancer control) to expand beyond the identification and avoidance of carcinogens. Specific interventions to prevent cancer in those at risk, and more sensitive and specific screening for early detection of cancer are the goals.
Cancer Screening Screening is a means of detecting disease early in asymptomatic individuals, with the goal of decreasing morbidity and mortality. While screening can potentially save lives and has been shown to do so in cervical, colon, and probably breast cancer, it is also subject to a number of biases that can suggest a benefit when actually there is none. Biases can even mask net harm. Early detection does not in itself confer benefit. To be of value, screening must detect disease earlier, and treatment of earlier disease must yield a better outcome than treatment at the onset of...
Potential Biases of Screening Tests The common biases of screening are lead time, length-biased sampling, and selection. These biases can make a screening test seem beneficial when actually it is not (or even causes net harm). Whether beneficial or not, screening can create the false impression of an epidemic by increasing the number of cancers diagnosed. It can also produce a shift in proportion of patients diagnosed at an early stage that improves survival statistics without reducing mortality (i.e.
Chemoprevention of Cancers of the Upper Aerodigestive Tract Smoking causes diffuse epithelial injury in the head, neck, esophagus, and lung. Patients cured of squamous cell cancers of the lung, esophagus, head, and neck are at risk (as high as 5% per year) of developing second cancers of the upper aerodigestive tract. Cessation of cigarette smoking does not markedly decrease the cured cancer patient's risk of second malignancy, even though it does lower the cancer risk in those who have never developed a malignancy.
Lung Cancer Chest x-ray and sputum cytology have been evaluated in randomized lung cancer screening trials. No reduction in lung cancer mortality has been seen, although all the controlled trials have had low statistical power. Even screening of high-risk subjects (smokers) has not proven beneficial. Spiral CT can diagnose lung cancers at early stages; however, false-positive rates are high. Spiral CT screening increases the number of lesions detected and increases the number of diagnostic and therapeutic procedures. However, its capacity to save lives is unproven.
Breast cancer remains a leading cause of cancer death among women
in the United States. More than 180,000 new cases of invasive breast
cancer are diagnosed each year, and more than 40,000 women die of the
disease. Recent years, however, have seen improvements in survival
attributed to better treatment and earlier diagnosis. Research efforts have
been directed toward better treatment, preventive strategies, and early
Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành y học dành cho các bạn tham khảo đề tài: Early detection of Varicella-Zoster Virus (VZV)-specific T-cells before seroconversion in primary varicella infection: case report
Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Early detection of urothelial premalignant lesions using hexaminolevulinate fluorescence cystoscopy in high risk patients
Breast 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.
Physical Activity Physical activity is associated with a decreased risk of colon and breast cancer. A variety of mechanisms have been proposed. However, such studies are prone to confounding factors such as recall bias, association of exercise with other health-related practices, and effects of preclinical cancers on exercise habits (reverse causality). Recommending adults to engage in at least 30 min of vigorous activity for ≥3 days a week is good health advice, though its effects on cancer incidence are unproven.
Cancer Chemoprevention Chemoprevention involves the use of specific natural or synthetic chemical agents to reverse, suppress, or prevent carcinogenesis before the development of invasive malignancy.
Cancer develops through an accumulation of genetic and epigenetic changes that are potential points of intervention to prevent cancer. The initial changes are termed initiation. The alteration can be inherited or acquired through the action of physical, infectious, or chemical carcinogens.
Chemoprevention of Breast Cancer Hormonal manipulation is being tested in the primary prevention of breast cancer. Tamoxifen is an antiestrogen with partial estrogen agonistic activity in some tissues, such as endometrium and bone. One of its actions is to upregulate transforming growth factor β, which decreases breast cell proliferation. In randomized placebo-controlled trials to assess tamoxifen as adjuvant therapy for breast cancer, tamoxifen reduced the number of new breast cancers in the opposite breast by more than a third.
Screening for Specific Cancers Widespread screening for cervical, colon, and likely breast cancer is beneficial for certain age groups. A number of organizations have considered whether or not to endorse routine use of certain screening tests. Because these groups have not used the same criteria to judge whether a screening test should be endorsed, they have arrived at different recommendations. The U.S. Preventive Services Task Force (USPSTF), the Canadian Task Force on Preventive Health Care, and the American Cancer Society (ACS) publish screening guidelines (Table 78-3).
Improved understanding of carcinogenesis has allowed cancer prevention and early detection (also known as cancer control) to expand beyond the identification and avoidance of carcinogens. Specific interventions to prevent cancer in those at risk, and more sensitive and specific screening for early detection of cancer are the goals. Carcinogenesis is not simply an event but a process, a continuum of discrete cellular changes over time resulting in more autonomous cellular processes.
Recent reductions in cancer mortality are
due in part to risk reduction behaviors like
smoking cessation and more strongly to early
detection of cancer coupled with appropriate
therapy. Yet, there are no validated molecular
biomarker tests for the early detection of any
cancer (see Table I). Among the list of Food
and Drug Administration (FDA)-approved
biomarkers, none have been approved for
cancer early detection and screening.
Tuyển tập các báo cáo nghiên cứu về y học được đăng trên tạp chí y học Wertheim cung cấp cho các bạn kiến thức về ngành y đề tài: Heart echinococcus cyst as an incidental finding: early detection might be life-saving...
The Book "Melanoma - From Early Detection To Treatment" is aiming to present data and knowledge from most experienced experts in the field. The book covers main topics from the fundamental aspects to multiple approaches in the disease treatment as well as related features. It offers a global view concerning one of the most frequent types of cancer to which a substantial high proportion of people worldwide is confronted at some time point in life.