Results of Breast Cancer Screening
Breast cancer screening programs have now been in place in many areas of the world for quite a number of years now, and the result invariably show a huge statistical reduction in breast cancer mortalities as the direct result of early diagnosis through breast cancer screening. The results of a typical organized breast cancer screening program are given in the tables below. Screening is often broken down into different age groups or perhaps by risk factors, but the results below are just a general, ‘across-the-board’ representations.
Please note: this old page from around year 2000, has been superceded by a new page on results of screening programs, which is a better page and up-to-date references.
Screening results in a typical organized program
Breast cancer screening statistics are uniformly positive. In addition to the actual rate of breast cancer detection, breast cancer screening statistics often reveal information about recall rate, detection of ‘in situ’ vs invasive breast cancer, and tumor size. It is also possible to estimate the reduction in breast cancer related mortalities as the direct result of screening and early detection programs for breast cancer.
Participation, Recall and Breast Cancer Detection Rate
Participation rate in breast cancer screening programs tends to be around 70%, even for those asked to participate. Some studies have even suggested that the actual breast cancer rate for the ‘random’ population would be even higher, for a variety of reasons. The recall rate (for follow up investigations and probably a biopsy) is typically just under 7%. Note, a vast majority of ‘suspicious findings’ on breast cancer mammography turn out to be benign. The actual rate of breast cancer detection is about 0.5%.
|Participation Rate||70% of those asked to participate|
|Recall Rate||< 7% on intial screening.||<5% on subsequent.|
|Cancer Detection Rate||about .5%||about 5 per 1000 women|
Ductal Carcinoma in situ and invasive Cancer
Ductal carcinoma in situ is an early stage breast cancer that hasn’t even entered the breast duct walls. The ‘cure rate’ for breast carcinoma discovered ‘in situ’ is close to 100%. About 25% of breast cancers detected in screening programs are DCIS. DCIS may or may not be found as a ‘lump’, and is far more likely to be detected mammographically, often by the presence of microcalcifications.
|DCIS Ductal carcinoma "in Situ"||approx. 20-25% of detected initial cancers|
|Invasive Cancer||approx. 75%|
Size of Tumor detected in intial screening
The stage and grade of a breast cancer tumor is largely determined by the microscopic/nuclear analysis of the tissue as well as the apparent ‘infiltrative’ status of the breast cancer cells, but also by the size of the tumor. Generally speaking, the larger the tumor has grown, the more difficult it is to cure. Statistically, invasive breast cancer tumors less than 10mm in diameter account for 30%-50% of tumors discovered on initial breast cancer screening, while larger tumors, greater than 15mm comprise around 50% of breast cancers initially detected through screening mammography. Mind you, a breast cancer tumor of 15mm is still considered to be very small and very treatable.
|Invasive Cancer. tumor < 10 mm||approx. 30-50% of detected intial cancers||1.5 per 1000 women|
|Invasive Cancer. Tumor < 15 mm.||Approx. 50% of detected intitial cancers||2.5 per 1000 women|
Node Negative Status
Of the cancers detected in the initial screening, ‘node negative’ status (indicating no involvement of the lymph nodes as of yet) was about 70%-75%. In other words, positive involvement or spread of breast carcinoma to the lymph nodes tends to be detected in about 25% of women screened for breast cancer. It is noteworthy that patients who are screened for breast cancer by clinical examination alone and not screening mammography are about 10% more likely to have developed positive lymph node involvement at the time of actual confirmed diagnosis of breast cancer.
Reduction in mortality
Based on this particular screening survey, it is estimated that the mortality reduction as a result of screening is as high as 40% over 10 years. Note that the cancer detection rate is about 5 per 1000 women, or 1 in every 250 women. It is of course preferable to intervene before the cancer has a chance to manifest as ‘cancer’, either ‘in situ‘ or as invasive cancer. The statistics show a recall rate of about 6%, which means that high risk factors or very very early cancer indicators are detected. Actual invasive or in-situ cancer is detected at about .5 percent, which suggests that about 83% of potential cancers for these women have been stopped or at least delayed, as a result of screening.
Studies have tended to show that organized breast cancer screening programs result in a reduction of breast cancer mortalities of about 25% to 40%. Through breast cancer screening, the number of stage II or higher breast cancers can be reduced by up to 30%. These results indicate a reduction in breast cancer mortality of between 40% and 45% in association with screening, after adjustment for self-selection bias. In practical terms, it is estimated that the number of women screened for breast cancer in order to positively identify and ultimately save the life of one woman, is about 470.
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