We tend to forget that science does not always represent “the truth” but is instead our best guess based on the data currently available. Much of our understanding of breast cancer comes from looking at cells under a microscope and predicting how they are going to behave. Based on this research, we have determined that breast cancer starts as an abnormality in the lining of a breast duct, somewhat like rust. It then eventually breaks out of the duct and moves into the surrounding breast tissue. From there, the cancer cells get into a blood vessel and spread to the rest of the body, ultimately causing death. We have also come to believe that if we can stop this progression by catching it early, we will keep a woman from dying from breast cancer.
A new study that appears today in the Journal of the American Medical Association calls this thinking into question.
The study, by a Canadian research group, used data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) registries to look at outcomes for 108,196 women who had been diagnosed with ductal carcinoma in situ (DCIS), the label we give to cells that look like breast cancer but are contained in the duct.
DCIS can initially appear as a breast lump but more commonly it is found on screening mammography as tiny specks, calls microcalcifications. Treatments for DCIS can range from mastectomy or even bilateral mastectomy to lumpectomy, with or without radiation. (I know it is crazy to call it a lumpectomy when in fact there is no lump but it is a tradition). Some women will then be treated with tamoxifen for five years. There have also been studies suggesting it may be even better to use an aromatase inhibitor. These treatment recommendations stem from studies that looked at how many woman had a recurrence of DCIS or breast cancer and required additional treatment.
This new study went right to the heart of the matter. It didn’t look at whether women had a recurrence; it looked at whether they died of breast cancer. It found that at 20 years after a DCIS diagnosis a woman’s overall chance of dying of breast cancer — regardless of the treatment she had or whether she had a recurrence — was about 3.3 percent. The chance of dying of something other than breast cancer was five percent!
There were some groups where the risk was higher: women who were diagnosed with DCIS before age 35 had a 7.8 percent risk of dying from breast cancer and for black women the risk was seven percent.
This suggests there are two kinds of DCIS. One that may recur in the breast but will probably not kill you and one which may look like DCIS but is actually an invasive cancer that may have already spread. The fact that the second type was more likely to be seen in younger women and in black women suggests this type may be more likely to present as a lump, but more research is needed to see if that is correct.
This new study also confirms that we are over treating mammographically detected DCIS with surgery, radiation, and hormone therapy. Watchful waiting might well be an option for many women. But before we can recommend that we will need to find a reliable way to determine which DCIS is actually invasive cancer.
To do that, we will need to finally figure out the anatomy of the breast ducts and develop reliable ways to image and monitor them — which is something Dr. Susan Love Foundation for Breast Cancer Research is committed to doing. If DCIS is really just like rust in the pipes, maybe the next step is to figure out how to squirt something like Drano down the duct and clean them out!
This study shows how important it is that we continue to do research to get closer to the truth!