Ductal carcinoma in situ (DCIS) is a very early stage non-invasive breast cancer. A diagnosis of DCIS indicates that breast carcinoma is present, but has not yet infiltrated the lining of the breast ducts. There are many different types and grades of DCIS, most of which are not life threatening. Prior to 1980, DCIS was rarely diagnosed. But with recent advances in breast cancer screening procedures and increased participation in screening mammography, DCIS now comprises up to 25% of all breast cancer diagnoses in the United States. Overall about 20% of new breast cancer diagnoses are given at the DCIS stage. The good news is that the survival rate when DCIS is diagnosed is close to 98%.
There are a number of ways to confirm DCIS, but it is mostly identified by the presence of certain patterns of microcalcifications on the mammogram. By contrast, invasive breast cancer is typically identified as a mass or architectural distortion on the mammogram.
In Canada, studies have shown that for women aged 50-69, of positive findings, an invasive tumor of less than 1.5 cm is detected about 54% of the time, with a 'node negative' status about 77 % of the time. (Node negative means that the cancer has not spread into the lymph nodes) This means that even if breast carcinoma is not diagnosed at the DCIS stage, the odds of discovering and successfully treating breast cancer at an early invasive stage are still very good.
The chart below, sampled between 1996 and 2003 in the USA, demonstrates the relative rates for DCIS as compared to full breast cancer remain about the same over time. It also shows that the total number of breast cancer and DCIS cases in that country tended to hover around 6000 women during that time period. Overall the ratio of DCIS to breast cancer for all age groups appears to be between 15% and 20%.
Initial screening for breast cancer sorted by different age groups underlines the fact that the earlier the screening begins, the rate of DCIS as compared to cancer will increases. In the graph below, one can observe that DCIS is most commonly diagnosed between the ages of 40 and 59, and is very uncommon for women under 30. This gives further support for breast cancer screening beginning at age 40 and continuing through the 50s. Most of the time, DCIS is a much better diagnosis and prognosis, resulting in fewer mortalities. In North America , initial screening procedures typically identify DCIS about 30% of the time for women over 40, as compared to 70% breast cancer diagnosis.
Invasive breast cancer rates did not increase during the late 1980s and have in fact declined since 2000. However, during this period the rate of DCIS diagnosis has increased by 200%. The use of screening mammography increased by approximately 250% during the same period, although with a peak increase much sooner than the increase of DCIS detection. The graphic below clearly demonstrates both the upward tradjectory of DCIS detection in the late 1980s, coinciding with improved screening procedures, and a peak and subsequent decline in invasive bresat cancer diagnosis since around 1998.
Over-diagnosis is a term now frequently associated with DCIS. Over-diagnosis means that the DCIS would not have otherwise been detected during a woman's lifetime without screening. In other words, the DCIS would not have posed any health problem. Between 15% and 18% of DCIS diagnoses are thought to be over-diagnosed. The concern is that a majority of DCIS cases are treated by surgery. In some instances DCIS has been treated by mastectomy when it may be completely unnecessary.
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