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Thread: Screening of Breast Cancer

  1. #1

    Default Screening of Breast Cancer

    Cancer screening refers to a test or examination performed on an asymptomatic individual. The goal is not simply to find cancer at an early stage, nor is it to diagnose as many patients with cancer as possible. The goal of cancer screening is to prevent death and suffering from the disease in question through early therapeutic intervention.
    Last edited by admin; Wed 13th January '16 at 6:24pm.
    Clinical Pharmacy Specialist - Hematology

  2. #2

    Exclamation Performance Characteristics

    The degree to which a screening test can discriminate between individuals with and without a particular disease is described by its performance characteristics. These include the a test's sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). It should be noted that these measures relate to the accuracy of a screening test; they do not provide any information regarding a test's efficacy or effectiveness.

    Screening of Breast Cancer-screen-shot-2015-12-26-at-1-32-48-pm-png

    For a given screening test, sensitivity and specificity are inversely related. For example, as one lowers the threshold for considering a serum prostate-specific antigen (PSA) level to represent a positive screen, the sensitivity of the test increases and more cancers will be detected. This increased sensitivity comes at the cost of decreased specificity (i.e., more men without cancer will have positive screenings tests and, therefore, will be subjected to unnecessary diagnostic procedures).

    Some screening tests, such as mammograms, are more subjective and operator dependent than others. For this reason, the sensitivity and specificity of screening mammography varies among radiologists. For a given radiologist, the lower his or her threshold for considering a mammogram to be suspicious, the higher the sensitivity and lower specificity will be for them. However, mammography can have both a higher sensitivity and higher specificity in the hands of a more experienced versus a less experienced radiologist.

    As opposed to sensitivity and specificity, the PPV and NPV of a screening test are dependent on disease prevalence. PPV is also highly responsive to small increases in specificity. As shown in Table 34.2, given a disease prevalence of 5 cases per 1,000 (0.005), the PPV of a hypothetical screening test increases dramatically as specificity goes from 95% to 99.9%, but only marginally as sensitivity goes from 80% to 95%. Given a disease prevalence of only 1 per 10,000 (0.0001), the PPV of the same test is poor even at high sensitivity and specificity. The positive association between breast cancer prevalence and age is the major reason why screening mammography is a better test (higher PPV) for women aged 50 to 59 than for women 40 to 49 years of age.

    Screening of Breast Cancer-screen-shot-2015-12-26-at-2-10-09-pm-png
    Last edited by CheneyHsiung; Sat 26th December '15 at 3:49pm.
    Clinical Pharmacy Specialist - Hematology

  3. #3

    Default Bias of Cancer Screening

    Lead time bias occurs whenever screening results in an earlier diagnosis than would have occurred in the absence of screening. Because survival is measured from the time of diagnosis, an earlier diagnosis, by definition, increases survival. Unless an effective intervention is available, lead time bias has no impact on the natural history of a disease and death will occur at the same time it would have in the absence of early detection.

    Length bias is a function of the biologic behavior of a cancer. Slower growing, less aggressive cancers are more likely to be detected by a screening test than faster growing cancers, which are more likely to be diagnosed due to the onset of symptoms between scheduled screenings (interval cancers). Length bias has an even greater effect on survival statistics than lead time bias.

    Overdiagnosis is an extreme form of length bias and represents pure harm. If refers to the detection of tumors, often through highly sensitive modern imaging modalities and other diagnostic tests, that fulfill the histologic criteria for malignancy but are not biologically destined to harm the patient.

    There are two categories of overdiagnosis: the detection of histologically defined cancers not destined to metastasize or harm the patient, and the detection of cancers not destined to metastasize or cause harm in the life span of the specific patient. The importance of this second category is illustrated by the widespread practice in the United States of screening elderly patients with limited life expectancies, who are thus unlikely to benefit from early cancer diagnosis.

    Stage shift. A cancer diagnosis at an earlier stage than would have occurred in the absence of screening is necessary, but not sufficient, for a screening test to be effective in terms of reducing mortality. Both lead time bias and length bias contribute to this phenomenon.

    Although it is tempting to speculate that diagnosis at an earlier stage must confer benefit, this is not necessarily the case. For example, a substantial proportion of men treated with radical prostatectomy for what appears to be a localized prostate cancer relapse after undergoing surgery. Conversely, some men who are treated with definitive therapy would never have gone on to develop metastatic disease in the absence of treatment.

    Selection bias occurs when enrollees in a clinical study differ from the general population. In fact, people who voluntarily participate in clinical trials tend to be healthier than the general population, perhaps due to a greater interest in health and healthcare research. Screening studies tend to enroll individuals healthier than the general population. This so-called healthy volunteer effect can introduce a powerful bias if not adequately controlled for by randomization procedures.
    Last edited by Janis.Y.Chen; Sat 26th December '15 at 6:43pm.
    Clinical Pharmacy Specialist - Infectious Diseases

  4. #4

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    Clinical Pharmacy Specialist - Infectious Diseases

  5. #5

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    Clinical Pharmacy Specialist - Infectious Diseases

  6. #6

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    Clinical Pharmacy Specialist - Infectious Diseases

  7. #7

    Default Recommendations for Breast Cancer Screening - Women at Average Risk

    The ACS (American Cancer Society) and most other medical groups recommend that average risk women undergo a CBE (clinical breast examinations) every 3 years starting at age 20 and that women 40 years of age and over should undergo CBEs and screening mammograms annually.

    Women should be informed of the benefits, limitations, and harms associated with breast cancer screening. A mammography will not detect all breast cancers, and some breast cancers detected with mammographies may still have a poor prognosis. The harm associated with breast cancer screening also include the potential for FP (false positive) results, causing substantial anxiety.

    When abnormal findings cannot be resolved with additional imaging, a biopsy is required to rule out the possibility of breast cancer. A majority of biopsies are benign.

    Finally, some breast cancers detected by a mammography may be biologically indolent, meaning they would not have caused a problem or have been detected in a woman's lifetime had she not undergone a mammography.
    Clinical Pharmacy Specialist - Infectious Diseases

  8. #8

    Default Recommendations for Breast Cancer Screening - Women at High Risk

    High risk women include (According to ACS):

    • With a known BRCA mutation
    • Who are untested but have a first-degree relative relative with BRCA mutation
    • Who had been treated with radiation to the chest for Hodgkin disease
    • Who have an approximately 20% to 25% or greater lifetime risk of breast cancer based on specialized breast cancer risk estimation models.


    For those individuals, ACS recommends annual screening mammographies and MRIs starting at age 30.

    PS: Breast Cancer Risk Prediction Models Breast Cancer Risk Prediction Models
    Last edited by Janis.Y.Chen; Sat 26th December '15 at 8:31pm.
    Clinical Pharmacy Specialist - Infectious Diseases

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