Breast cancer screening with mammography or other tools (such as MRI) has increased the rates of diagnosis of very early breast cancers knowns as DCIS (ductal carcinoma in situ). As opposed to invasive breast cancers, DCIS cancers are confined to the local area and have not spread to deeper tissues or elsewhere in the body. With increased rates of diagnosis, there has been considerable controversy about the true risks of DCIS and the best treatments, with some suggesting that women are being overtreated for a condition that does not substantially increase the long-term risk of death, and others advocating more intensive preventive treatment among women with DCIS.
Long-term outcomes for women with and without DCIS have been limited, until now
A recent study published in The BMJ offers the best data so far on the risks associated with DCIS and the impact of different treatments. In the study, more than 35,000 women diagnosed with DCIS via mammography were followed for up to 20 years to see if they developed invasive breast cancer or died of breast cancer.
Overall, the researchers found that having DCIS more than doubled the risk of developing invasive breast cancer and increased the risk of dying of breast cancer by 70%, compared with the general population. Moreover, the researchers observed that more intensive treatment of DCIS was associated with lower risk of invasive breast cancer. Compared to women who had both breast-conserving surgery (lumpectomy) and radiation therapy, those who had lumpectomy alone had 43% higher rates of breast cancer, and those who had mastectomy had 45% lower rates of breast cancer. A larger DCIS-free margin in the biopsy sample was also associated with lower rates of developing invasive breast cancer. For women with estrogen receptor-positive DCIS, hormone treatment to reduce estrogen levels was associated with lower