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Screening
By admin | December 9, 2007
Breast cancer screening is an attempt to find unsuspected cancers. The most common screening methods are self and clinical breast exams, x-ray mammography, Breast Magnetic resonance imaging (MRI), ultrasound, Miraluma and genetic testing.
X-ray mammography
Mammography is still the modality of choice for screening of early breast cancer, since it is relatively fast, reasonably accurate, and widely available in developed countries. Breast cancers detected by mammography are usually much smaller (earlier stage) than those detected by patients or doctors as a breast lump.
Due to the high incidence of breast cancer among older women, screening is now recommended in many countries. Recommended screening methods include breast self-examination and mammography. Mammography has been estimated to reduce breast cancer-related mortality by 20-30%. Routine (annual) mammography of women older than age 40 or 50 is recommended by numerous organizations as a screening method to diagnose early breast cancer and has demonstrated a protective effect in multiple clinical trials. The evidence in favor of mammographic screening comes from eight randomized clinical trials from the 1960s through 1980s. Many of these trials have been criticised for methodological errors, and the results were summarized in a review article published in 1993.
Improvements in mortality due to screening are hard to measure; similar difficulty exists in measuring the impact of Pap smear testing on cervical cancer, though worldwide, the impact of that test is likely enormous. Nationwide mortality due to cancer before and after the institution of a screening test is a surrogate indicator about the effectiveness of screening, and results of mammography are favorable.
The U.S. National Cancer Institute recommends screening mammography every one to two years beginning at age 40. In the UK, women are invited for screening once every three years beginning at age 50. Women with one or more first-degree relatives (mother, sister, daughter) with premenopausal breast cancer should begin screening at an earlier age. It is usually suggested to start screening at an age that is 10 years less than the age at which the relative was diagnosed with breast cancer.
A clinical practice guideline by the US Preventive Services Task Force recommended “screening mammography, with or without clinical breast examination (CBE), every 1 to 2 years for women aged 40 and older.” The Task Force gave a grade B recommendation. (verification needed)
Criticisms of screening mammography
Several scientific groups however have expressed concern about the public’s perceptions of the benefits of breast screening. In 2001, a controversial review published in The Lancet claimed that there is no reliable evidence that screening for breast cancer reduces mortality. The results of this study were widely reported in the popular press.
False positives are a major problem of mammographic breast cancer screening. Data reported in the UK Million Woman Study indicates that if 134 mammograms are performed, 20 women will be called back for suspicious findings, and four biopsies will be necessary, to diagnose one cancer. Recall rates are higher in the U.S. than in the UK. The contribution of mammography to the early diagnosis of cancer is controversial, and for those found with benign lesions, mammography can create a high psychological and financial cost.
Mammography in women less than 50 years old
Part of the difficulty in interpreting mammograms in younger women stems from the problem of breast density. Radiographically, a dense breast has a preponderance of glandular tissue, and younger age or estrogen hormone replacement therapy contribute to mammographic breast density. After menopause, the breast glandular tissue gradually is replaced by fatty tissue, making mammographic interpretation much more accurate. Some authors speculate that part of the contribution of estrogen hormone replacement therapy to breast cancer mortality arises from the issue of increased mammographic breast density. Breast density is an independent adverse prognostic factor on breast cancer prognosis.
A systematic review by the American College of Physicians concluded “Although few women 50 years of age or older have risks from mammography that outweigh the benefits, the evidence suggests that more women 40 to 49 years of age have such risks”.
A report released November 27, 2007 by the Journal of the National Cancer Institute showed that the formula doctors use to calculate a woman’s risk of breast cancer underestimates the danger for black women most of the time and especially for those age 50 and older — the age when they are most likely to benefit from screening tests and protective drugs, according to the first major reassessment of the widely used tool.
Enhancements to mammography
In general, digital mammography and computer-aided mammography have increased the sensitivity of mammograms, but at the cost of more numerous false positive results.
Computer-aided diagnosis(CAD) Systems may help radiologists to evaluate X-ray images to detect breast cancer in an early stage.[citation needed] CAD is especially established in US and the Netherlands. It is used in addition to the human evaluation of the diagnostician.
Breast MRI
Magnetic resonance imaging (MRI) has been shown to detect cancers not visible on mammograms, but has long been regarded to have disadvantages. For example, although it is 27-36% more sensitive, it is less specific than mammography. As a result, MRI studies will have more false positives (up to 5%), which may have undesirable financial and psychological costs. It is also a relatively expensive procedure, and one which requires the intravenous injection of a chemical agent to be effective. Proposed indications for using MRI for screening include:
* Strong family history of breast cancer
* Patients with BRCA-1 or BRCA-2 oncogene mutations
* Evaluation of women with breast implants
* History of previous lumpectomy or breast biopsy surgeries
* Axillary metastasis with an unknown primary tumor
* Very dense or scarred breast tissue
However, two studies published in 2007 demonstrated the strengths of MRI-based screening:
* In March 2007, an article published in the New England Journal of Medicine demonstrated that in 3.1% of patients with breast cancer, whose contralateral breast was clinically and mammographically tumor-free, MRI could detect breast cancer. Sensitivity for detection of breast cancer in this study was 91%, specificity 88%.
* In August 2007, an article published in The Lancet compared MRI breast cancer screening to conventional mammographic screening in 7,319 women. MRI screening was highly more sensitive (97% in the MRI group vs. 56% in the mammography group) in recognizing early high-grade Ductal Carcinoma in situ (DCIS), the most important precursor of invasive carcinoma. Despite the high sensitivity, MRI screening had a positive predictive value of 52%, which is totally accepted for cancer screening tests. The author of a comment published in the same issue of The Lancet concludes that “MRI outperforms mammography in tumour detection and diagnosis.”
Breast ultrasound
Ultrasound alone is not usually employed as a screening tool but it is a useful additional tool for the characterization of palpable tumours and directing image-guided biopsies. Using an ultrasound allows a look at dense breast tissue which is not possible with digital mammmography. It is closely correlated with the digital mammography. The other significant advantage over digital mammography is that it is a pain-free procedure.
Breast-specific gamma imaging
Breast-Specific Gamma Imaging (BSGI, also called Miraluma) is a breast imaging procedure that reflects the metabolic activity of breast lesions. Most (not all) malignant tumors show a higher metabolic activity than normal tissue, a reflection of their faster growth rate and of their abnormal metabolism (see the Warburg hypothesis). A small amount of Technetium 99 linked to six molecules of MIBI (Tc99m-sestamibi) is injected intravenously to a patient. The highly metabolic tumors absorb a greater amount of the tracing agent and appear as “hot spots” on the image produced by a gamma camera.
Breast self-exam
Breast self-examination was widely discussed in the 1990s as a useful modality for detecting breast cancer at an earlier stage of presentation. A large clinical trial in China reduced enthusiasm for breast self-exam. In the trial, reported in the Journal of the National Cancer Institute first in 1997 and updated in 2002, 132,979 female Chinese factory workers were taught by nurses at their factories to perform monthly breast self-exam, while 133,085 other workers were not taught self-exam. The women taught self-exam tended to detect more breast nodules, but their breast cancer mortality rate was no different from that of women in the control group. In other words, women taught breast self-exam were mostly likely to detect benign breast disease, but were just as likely to die of breast cancer.
Topics: breast cancer |
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