The Epidemiology of Breast Cancer

According to the World Health Organization, breast cancer is the most prevalent cause of cancer-related deaths among women worldwide. More than 1.1 million women worldwide are newly diagnosed with breast cancer annually. This represents about 10% of all new cancer cases and 23% of all female cancers. With more than 500,000 deaths each year, breast cancer accounts for about 15% of all female cancer deaths and 1.7% of all female deaths worldwide.

A recent report by the American Cancer Society has indicated that approximately every three minutes a woman in the United States is diagnosed with breast cancer. If Ductal Carcinoma in situ (DCIS) is counted, more than 12 million cases worldwide and more than 270,000 cases in the USA are diagnosed each year. In 2007, an estimated 213,000 new cases of invasive breast cancer were diagnosed in the USA, along with 62,000 new cases of non-invasive breast cancer. An estimated 200,000 American women are expected to develop invasive breast cancer in 2012, and more than 44,000 will die from the disease this year. Although there has been a reported reduction in the number of invasive breast cancers (perhaps due to extensive screening, which allows for early detection and successful treatment), there is still a long way to go in containing the disease and improving its treatment. To date, there are over 2.2 million women living in the United States who have been treated for breast cancer with staggering financial implications. According to the latest estimates provided by the National Cancer Institute, the annual expenditures for breast cancer treatment in the US alone exceed $8.1B.

The key to surviving breast cancer is early detection of abnormal signs and effective treatment. According to the American Cancer Society, when breast cancer is confined to the breast (without spreading to other organs), the five-year survival rate is close to 100%. This is an important indication that early detection of breast cancer is crucial in reducing the need for therapeutic treatments and minimizes the pain and suffering, allowing patients to continue leading healthy and productive lives. However, several recent published statistics in the American Journal of Roentgenology and elsewhere have disturbing implications for breast imaging. They present a worrisome steady decline in the number of women who are undergoing mammography screening and a looming workforce shortage as many imaging professionals shun careers in mammography, while at the same time an aging population promises to drive up demand for screening.
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Definitions in Breast Imaging

  • False Positives (FP)
    There is no malignant tumor in the breast, but the test mistakenly points at malignancy.
  • False Negatives (FN)
    There is cancerous tumor in the breast, but the test mistakenly indicates of no malignancy.
  • True Positive (TP)
    The test indicates presence of breast cancer, and there is actually malignant tumor in the breast.
  • True Negative (TN)
    There is no malignant tumor in the breast, and the test does not indicate presence of any cancerous tumor.
    Test is Positive Test is Negative
    Patient is Positive True Positive (TP) False Negative (FN)
    Patient is Negative False Positive (FP) True Negative (TN)
  • Sensitivity
    The Sensitivity of a test is the proportion of those who have been tested positive for breast cancer among all those with breast cancer. For example, if a test has high sensitivity then a negative result would suggest the absence of cancerous tumor:
  • Specificity
    The Specificity of a test is the proportion of those who have tested negative for breast cancer and actually does not have breast cancer. For example, if a test has high specificity, a positive result from the test means a high probability of the presence of cancerous tumor:
  • Positive Predictive Value (PPV)

    Overwhelming majority of women who undergo breast screening do not have cancer, and only a few have malignant tumors. Even in a test with high specificity, where only a small fraction of the women with benign tumors have been misdiagnosed for malignancy, there are so many more healthy women than women with cancer that the false positives can actually outnumber the true positives. This means that if one is initially diagnosed for malignancy, there is actually a good chance that there will be no cancerous tumor.

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  • Breast Imaging and Data System (BI-RADS) Lexicon
    The ACR BI-RADS lexicon enables radiologists to use standardized terminology to describe mammographic findings. This lexicon facilitates data tracking and provides clear management and follow-up recommendations to referring physicians, allied healthcare providers, and patients. There are 6 ACR BI-RADS categories:

    Category 0, or "need additional imaging evaluation," is used if additional imaging is needed. This category is almost always used in a screening situation and should be used only rarely after a full imaging workup. Additional imaging evaluation includes the use of spot compression and magnification views, along with other tailored mammographic views and ultrasound imaging.

    Category 1, or "negative," is used if there are no findings to comment on. For example, the breasts are symmetrical, and no masses, architectural disturbances, or suspicious calcifications are present.

    Category 2, or "benign finding," is used if the radiologist wishes to describe a benign finding while still concluding that there is no mammographic evidence of malignancy.

    Category 3, or "probably benign finding–short-term interval follow-up suggested," is used when a noted finding has a very high probability of being benign. The finding is not expected to change over the follow-up interval, but the radiologist prefers to establish its stability over time.

    Category 4, or "suspicious abnormality–biopsy should be considered," is used when a finding has a definite probability of being malignant.

    Category 5, or "highly suggestive of malignancy–appropriate action should be taken," is used when a finding has a high probability of being cancerous.

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