Breast Cancer Screening Results
Breast cancer early-detection screening programs have been implemented in various countries over the last 20 to 30 years. The results tend to be fairly consistent in terms of actual breast cancers detected. Even though the percentage of women screened who actually present at screening with breast cancer is very low, when this percentage is multiplied by the massive numbers of women now participating in screening programs it results in a huge decrease in mortality due to breast cancer.
From now on, make sure you keep in mind that this page is getting a little bit older, whereas this introduction to screening page is brand spankin’ new.
Breast Cancer screening results taken from Sweden, other European Countries, United Kingdom, and Australia, give a fairly good representation of typical cancer detection rates. The age range for the surveys discussed here is not standard, but is between 50-69. (Screening is typically recommended for women starting at the age of 40, and sooner if there are high risk factors.)
Participation rate in breast cancer screening programs
The rate of voluntary participation in breast cancer screening rates tends to range between 60% to 70%. Generally speaking, the more educated a women is with regard to her overall health generally, the more likely that she will participate in a breast cancer screening program. Studies have suggested that women who voluntarily participate in breast cancer screening programs are more health-wise, generally, than those who do not. The rate of breast cancer detection would probably be a little higher if women who are naturally ‘less-motivated’ were compelled to participate.
Recall rate (some abnormality or concern detected)
A woman may be ‘recalled’ following a screening mammogram is a suspicious finding is detected. Most suspicious mammograms turn out to be due to benign causes. Of particular concern are the presence of microcalcifications, areas of increased density, and any apparent lesion with ill-defined borders and an irregular shape. The recall rate from initial breast cancer screening tends to be between 7% and 9%. , with call backs from additional annual screenings about 5% to 7%.
|recall from initial screen||9%||7%||10%||10%|
|recall from subsequent screen||(na)||5%||7%||5%|
Invasive Cancer Detection Rate
The rate for detection of invasive breast cancers on initial breast cancer screening mammogram tends to be, for known statistics from developed nations, around 0.3%.
|At initial screening||3 times expected incidence rate||3 times expected incidence rate||2.7 women per 1000||50 women per 10,000|
|At a subsequent screening||(na)||1.5 times expected incidence rate||3 women per 1000||20 women per 10,000.|
The statistics regarding cancer incidence and detection rates are not standard for all countries. The Swedish and European figures are expressed as a multiple of the ‘expected incidence rate’ without screening, which is a bit confusing. Breast cancer not detected through routine screening will most likely be detected either by a breast self examination, or through a routine physical with a family physician. In both cases, breast cancer which has progressed to a ‘clinically palpable’ stage, ( such as a ‘lump’ ) is typically much more advanced and difficult to treat than cancers detected through mammography. The figure is really saying that very small invasive cancers are approximately 3 times as likely to be detected through screening than by other, more passive measures.
The UK figure ‘initial screening’ rate is expressed per 1000 women, while the Australian figure is per 10,000 women. 2.7 per 1000 is about 0.27 %, while 50 per 10,000 is about 0.5%. It should be noted that the above table concerns invasive cancer only, and does not include the more ambiguous, earlier stage expression of Ductal Carcinoma in Situ, or DCIS.
Ratio of benign to malignant tumors
If a tumour of a sufficient size is found, perhaps along with other indicators, a biopsy is usually taken. The following data represents the ratio of benign to malignant tumors as discovered through biopsy. It is far more likely that a suspicious finding sent for biopsy will turn out to be a benign breast disease unrelated to cancer. However, the ratio of benign vs malignant findings on subsequent annual breast screening mammograms tends to even out.
|At initial screening||3:1||2:1||(NA)||2:1|
|At a subsquent screening||(NA)||1:1||(NA)||1:1|
Size of invasive tumors
The size of the tumor at initial screening is an important factor in determining the seriousness of the disease and the appropriate treatment measures. The benchmark indicator for tumor size is whether or not it is less than 10mm in diameter, with 15mm being a second, important benchmark. Generally speaking, it would appear that about 25% of breast cancers discovered on initial screening are less an 10mm.
|less than 10 mm At initial screening||25% ( of initial detected cancers)||8 per 10,000 ( out of all women screened, not just detected cancers.)
( about .16%)
|less than 15 mm at initial screening||50% ( of initial detected cancers )||–||1.5 per 1000. (out of all women screened, not just detected cancers
|less than 15 mm on subsequent screening||–||–||1.65 per 1000||–|
A quick note on the ‘Australian’ figure. If the initial invasive cancer detection rate was 50 per 10000, and the rate of tumor size less than 10 mm is 8 per 10000, that’s about 0.16%. The UK figure of 1.5 women per 1000 less than 15mm is about 0.15%. In other words, of all women screened for breast cancer, the number of women who present with actual breast cancer tumors 15mm or less, is about 0.15%.
Ductal Carcinoma in situ. ( DCIS )
A finding of DCIS is a composite of many factors, and many physicians refer to different stages within DCIS. But, the general sense of the term is one in which cancer is detected within the epithelial lining of the ductal wall, but has not yet broken through or ‘infiltrated’ to the duct itself. The prognosis for breast carcinomas discovered at a ‘ductal carcinoma in situ‘ stage, is almost 100% positive. Statistics tend to agree on a DCIS detection rate of about 20% of all discovered breast cancers.
|DCIS detected in initial screening||0.4-0.9 per 1000 ( of all women screened )||10-20% ( of detected invasive cancers)|
|DCIS detected in subsequent screening||0.5 to 1.0 per 1000|
“Interval Cancer” means that cancer is detected on a subsequent screening, which was absent on the initial or previous screenings. It is, in effect, an indication of false negative screening results, and very aggressive breast cancers. It can be estimated that around 0.1% only of women who have no breast cancer detectable on initial screening will show breast cancer on a subsequent screening. However, it can also be stated that a woman’s risk of developing breast cancer increases with age, so annual to biannual check ups are naturally advised.
|Interval Cancer detected on subsequent screen||1.2 per 1000 women, within 2 years. (0.12 % of all women screened )||about 6 per 10,000 women, within 1 year. (about 0.06 % of all women
Breast Cancer screening programs in other areas of the world
A recent breast cancer screening and mortality study from the Netherlands showed results consistent or slightly higher than the global average, with about 0.7% of women screened referred for biopsy, and a confirmed breast cancer diagnosis rate of about 0.3%. New breast cancer screening programs have also begun in the middle east. A recent breast cancer screening program in Saudi Arabia resulted in a breast cancer detection rate of approximately 15 cases per 1000 women, or about 0.15%.
However, in impoverished nations, it is really not feasible to imagine the implementation of mammography based breast cancer screening programs in the foreseeable future. Effective breast cancer screening programs require a well organized and well funded approach, which has unfortunately tended only to be possible in the more developed nations. This is unfortunate, as it is estimated that, globally, about 70% of deaths due to cancer occur in low income, developing nations.
The overall/global reduction in breast cancer mortality due to early detection screening
Of course, the reduction in breast cancer related deaths as a result of breast cancer screening programs cannot be equated for all studies in the world. However, as a ‘ballpark’ figure, it would appear that breast cancer mortalities may be reduced in the order of 21% to 25% as a direct result of participation in screening mammography.
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