Description
The goal of cancer screening is to identify cancers when they are small and easier to treat, which can increase the chances of survival. There are different types of cancer screening tests available, including imaging tests (such as mammograms or CT scans), blood tests, and tissue samples (such as Pap smears or colonoscopies). The frequency of cancer screening depends on various factors, including age, gender, family history, and personal medical history. False positive results can occur in cancer screening tests, which can lead to unnecessary follow-up procedures and anxiety. False negative results can also occur, which means that a cancer may be missed by a screening test.
Résumé
- Cancer screening involves tests or examinations on asymptomatic individuals to prevent death and suffering through early therapeutic intervention. The goal is to detect diseases at an early stage when treatment can be more effective. Screening is classified as either opportunistic (performed at the discretion of a healthcare provider) or programmatic (a standardized approach with algorithms for screening and follow-up).
- An effective screening program requires diseases with a long preclinical phase, allowing time for intervention. It's important to distinguish between lead time bias (detecting a disease earlier) and length bias (detecting slower-growing cancers). Overdiagnosis, an extreme form of length bias, can occur when screening detects cancers that would regress spontaneously, potentially leading to unnecessary treatment.
- Key statistical terms used in screening include sensitivity (the proportion of individuals with the disease who test positive), specificity (the proportion of individuals without the disease who test negative), positive predictive value (the proportion of individuals with a positive test who actually have the disease), and negative predictive value (the proportion of individuals with a negative test who do not have the disease). A screening test should have high sensitivity to detect as many cases as possible, even if it means a lower specificity.
- For breast cancer screening, self-examination alone is not a recommended screening tool. Mammography is the primary screening tool for women over 40. Women at high risk (over 20% lifetime risk) should undergo annual MRI screening from age 30. The BI-RADS system (Breast Imaging Reporting and Data System) is used to standardize reporting of breast imaging results.
- Colorectal cancer screening is highly effective due to the adenoma-carcinoma sequence. Screening options include fecal occult blood tests (FOBT), flexible sigmoidoscopy, and colonoscopy. Screening should begin at age 50 for individuals at average risk and earlier for those with a family history of the disease.
- Cervical cancer screening is done using Pap smears (conventional cytology or liquid-based cytology). Women should be screened with cytology every three years, or with HPV testing and cytology every five years.
- No screening test is effective for detecting ovarian and endometrial cancers in the asymptomatic population. However, high-risk individuals (e.g., BRCA1/2 mutations, HNPCC) may benefit from annual rectovaginal pelvic examinations, CA-125 testing, and transvaginal ultrasound for ovarian cancer, and endometrial biopsy for endometrial cancer.
- Lung cancer screening using low-dose CT scans is recommended for high-risk individuals (age 55-74 with a significant smoking history). Prostate cancer screening with PSA testing should begin at age 50 after discussing the pros and cons with the patient, earlier for high-risk groups.
- Risk-reducing surgeries can be performed to prevent cancer development. These include salpingo-oophorectomy for BRCA-positive patients, colectomy for familial adenomatous polyposis, and prophylactic total gastrectomy for hereditary diffuse gastric cancer.
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