מידע על גילוי ואבחון סרטן שד - באנגלית
By: Prof. Yacov Itzchak
The Epidemiology of Breast Cancer
According to the World Health Organization, breast cancer is the most common cause of cancer-related deaths among women worldwide. More than 1.1 million women world-wide 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 410.000 deaths each year, breast cancer accounts for about 14% of all female cancer deaths and 1.6% 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. In 2006, an estimated 213.000 new cases of invasive breast cancer were diagnosed, along with 61.980 new cases of non-invasive breast cancer. 40.970 women dies in 2006 from this disease. About 178.480 women in the United States are expected to have invasive breast cancer in 2007, and about 40.460 women will die from the disease this year.
Although there has been a reported reduction 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 million women living in the United States who have been treated for breast cancer with staggering implications. According to the latest estimates provided by the National Cancer Institute, the annual expenditure for breast cancer treatment in the US alone exceed $8.1 billion.
The key to surviving breast cancer is early detection 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.
The Current Status of Breast Screening Practice and modalities
There are differences in recommendations on screening healthy women for breast cancer worldwide. These differences are mainly attributed to the variations in interpretation of cost-benefit analyses. While in Europe women over 50 are recommended to have a mammography every two years, the American Cancer Society recommends that women aged 40 and older have a clinical breast examination and mammogram once a year. Women with a family history of breast cancer are referred to early detection examinations, including use of diagnosis modalities such as X-ray mammography, 2-dimensional ultrasound, magnetic resonance imaging (MRI) and MRI with CAD.
Despite significant advances in these modalities, they have failed to provide an adequate and complete solution for the screening of the healthy female population either due to technological barriers or because of their prohibitively high cost. An ideal imaging modality would identify abnormal tissue characterize and localize the abnormalities within the breast and facilitate further examination or treatment.
Imaging methodologies are conventionally used to map and differentiate structural differences in tumors, such as micro-calcifications, tissue masses, angiogenesis, asymmetries, and architectural distortions to biologically or functionally distinguish between tumors and normal tissues. To date, the method of choice for diagnostic breast imaging has been X-ray mammography. In cases where diagnosis by mammography is not specific or in women at high risk, additional examinations by ultrasound or MRI are required. When mammograms result in positive diagnosis, a pathological biopsy test is performed to determine whether the detected lesion or tumor is benign or malignant.
Non invasive Diagnosis Technologies
The following sections provide grief summaries of all methods for breast imaging.
Mammography - to date, X-ray mammography is the method of choice and "gold standard" for breast screening and diagnosis (for more details see Appendix A). during the past fifteen years, mammography screening has reduced the mortality among women with breast cancer considerably, by detecting approximately 85% to 90% of breast cancers. Mammography imaging is X-ray based and provides reasonable spatial resolution, allowing for the detection of micro-calcifications and morphological modifications (asymmetry, ill-defined boundaries, among other parameters). The procedure is rapid, cost-effective (mammography -detected cancer treatment cost approximately $8.000 less than cancers diagnosed later with non-screening methods), and generally accurate and consequently is universally employed as the gold standard screening technology. However, there are several recognized weaknesses in mammography screening.
Conventional 2-dimensional and 3-dimentsional Ultrasound Imaging:
Ultrasound screening is usually done in cases of dense breast, or implants when mammography may not be useful in identifying breast lumps. It is also in wide use in guided biopsy since is allows real time imaging of the breast.
Magnetic Resonance Imaging (MRI) - MRI can detect otherwise occult breast cancer but is prohibitively expensive and unsuitable for large scale screening programs.
The prevalence of cancer at MRI screening in high risk women is significantly greater than that reported in a similar population screened by mammogram and ultrasound A number of a studies showed that the addition of MRI more than doubled the screening test sensitivity. Standardized as of today leading to variability I performance and in results interpretation. MRI can only be performed I a setting in which it is possible to perform biopsy of lesions detected solely by MRI.
Computed -aided Diagnosis (CAD) - CAD technology works basically like a second pair of eyes, reviewing a patient's mammogram film after the radiologist has already provided an initial interpretation. The software is designed to mark any detected breast abnormalities or "regions of interest (ROI)" on the mammogram film. Thus, in addition to its clinical advantages, CAD could also provide radiologists with an edge of liability. However, in a 2005 study published in the European Journal of Radiology, researches found that CAD was able to correctly mark cancers that junior (inexperienced ) radiologists tended to miss more than for senior (experienced) radiologists.
Thermo/Photo-Acoustic Breast Imaging - Thermo/Photo Acoustic techniques detect breast abnormalities. Like optical mammography, thermo/photo acoustic probes the optical contrast of the tumor site with respect to surrounding tissue. The information on optical absorption in homogeneities is carried to the breast surface by ultrasound waves which have high attenuation and scattering in soft tissue, resulting in poor sensitivity. Both thermo and opt-acoustic techniques retain 3-D structural information of the targeted area. One of the major disadvantages of these techniques is the difficulties in displaying and analyzing the 3-D information retained from the targeted area. Therefore the time and cost required for image retrieval and analysis are potentially greater when compared with that of X-ray mammography and ultrasound.
Invasive Diagnostic Technology-Guided Biopsy -
Many biopsy methods rely on image guidance to help the radiologist or breast surgeon to precisely locate the lesion within the breast. Imaging may be necessary when a lesion cannot be felt during physical examination and is only detected through examination by mammography, MRI or ultrasound. It may also be necessary to use imaging to assure that a mass felt during examination is indeed the same abnormality noted on a mammogram, MRI or ultrasound. If image guidance is required, the consideration typically focuses on what type of image guidance is most appropriate for the biopsy.
Often' a woman receives a breast biopsy after discovery of a suspicious lesion by mammography or physical exam. However, only a low percentage of women undergoing biopsy actually have breast cancer. The positive predictive value of mammography has been estimated to be less than 30% and possibly as low as 15%. Only 20% of the biopsies result in positive diagnosis of a malignant lesion. Therefore, about 80% of the breast biopsies performed in US result in negative results. The imaging technologies available to date for guided biopsies are: X-ray (streo-tactic), ultrasound and MRI. MRI is utilized when ultrasound or mammogram (streo-tctic) guided biopsy is not specific in screening areas of interest. As mentioned above, the conventional 2-D ultrasound imaging lacks the adequate specificity while MRI bears high costs.
