Radiation Therapy for Ductal Carcinoma In Situ (DCIS)

Diana Zuckerman, PhD, Cancer Prevention and Treatment Fund.


In recent years, ductal carcinoma in situ (DCIS) has become one of the most commonly diagnosed breast conditions. It is often referred to as “stage zero breast cancer” or a “pre-cancer.” It is a non-invasive breast condition that is usually diagnosed on a mammogram when it is so small that it has not formed a lump. In DCIS, some of the cells lining the ducts (the parts of the breast that secrete milk) have developed abnormally, but the abnormality has not spread to other breast cells.

DCIS is not painful or dangerous, but it sometimes develops into breast cancer in the future if it is not treated. If it develops into breast cancer, it can spread.  If that happens, it is called invasive breast cancer. The goal of treating invasive cancer is to prevent it from spreading to the lungs, bones, brain, or other parts of the body, where it can be fatal. Since DCIS is not an invasive cancer, it is even less of a threat than Stage 1 or Stage 2 breast cancer, which are the earliest types of invasive cancer.1  For more information, see our free DCIS booklet, and our other articles on DCIS.

Most women with DCIS will never develop invasive cancer whether they are treated or not.  Unfortunately, it is impossible to predict which women with DCIS will develop cancer and which ones won’t. That’s why treatment is recommended. A woman with DCIS does not need all the same treatments as a woman diagnosed with invasive breast cancer, but surgery is almost always recommended. Most DCIS patients will choose a lumpectomy (which removes the DCIS but does not remove the entire breast), and radiation therapy is usually recommended for those women to destroy any stray abnormal cells in the same breast.1

Is Radiation Necessary?

Doctors usually recommend radiation therapy for lumpectomy patients, but since it is inconvenient and has some side effects, many women prefer to avoid it.  In fact, some DCIS patients decide to have a mastectomy because they do not want to undergo radiation.  However, mastectomy is a much more radical surgery and is very rarely a good idea for DCIS patients. That’s because almost all women with DCIS live long lives, and undergoing radiation does not affect whether DCIS patients live a long life or not.

Instead, the main advantage of radiation for DCIS is to prevent recurrence of DCIS in the breast where the DCIS was removed. A study of more than 1,700 women with DCIS who underwent a lumpectomy evaluated different treatment options.  The women were randomly assigned either to radiation, tamoxifen, radiation plus tamoxifen, or no treatment after surgery.  Undergoing radiation had a very small benefit for women in general, and has little impact on your chances of living a cancer-free life.

In women treated with radiation, about 10% developed DCIS or breast cancer within the next 10 years after surgery, and it made no difference whether these women took tamoxifen or not. And while the vast majority of women were alive 10 years later, their chances of survival were no different whether they were treated with radiation, tamoxifen, both, or neither.4  

For women who did not have radiation therapy, tamoxifen reduced the chances of developing DCIS within 10 years in the same breast by about 3% and the chances of developing DCIS in the other breast by about 1%. Tamoxifen did not significantly decrease the chances of developing invasive breast cancer in the same breast, and only reduced the chances of developing invasive cancer in the opposite breast by about 1%.4

So why do doctors so strongly recommend radiation and hormone therapy for DCIS?  Doctors tend to focus on reducing “relative risk” rather than actual risk. So, if a  treatment decreases the chances of recurrence by about 50% that sounds impressive — but 50% of a 16% chance is 8%, for example, and that isn’t much of a difference. And 50% of a 6% chance of recurrence is even less meaningful.  Most important, it doesn’t affect survival so women can skip radiation now and choose it later if they have a recurrence. In contrast, if a woman has radiation after a lumpectomy and later has a recurrence anyway, she can’t undergo radiation again.

When is radiation most important for DCIS?  It is more likely to benefit younger women (especially women diagnosed before age 40), women with more serious types of DCIS (a high grade DCIS called comedo), and women with a family history of breast cancer.

What is the benefit of hormone therapy for women also undergoing radiation therapy?

Tamoxifen blocks the effects of estrogen on breast cells, which can stop the growth of cancer cells that are sensitive to estrogen. A study of more than 1,800 pre-menopausal and post-menopausal women with DCIS evaluated the benefits of tamoxifen for women who had lumpectomy and radiation treatment. These women were randomly assigned to take tamoxifen for 5 years or a placebo (sugar pill). The study found that after 5 years, women who took tamoxifen were about 5% less likely to develop either DCIS or cancer in the same breast, cancer in the opposite breast, or distant cancer spread.  The difference was 8 of women taking tamoxifen compared to 13% of women taking placebo. However, the vast majority of women survived and they did not live any longer whether they took tamoxifen or not.1

For postmenopausal women, aromatase inhibitors may be used instead of tamoxifen. Aromatase inhibitors block the body’s ability to make estrogen. A study of more than 3,000 post-menopausal women with DCIS evaluated the benefits of hormone treatment for women who had lumpectomy and radiation treatment. These women were randomly assigned to take tamoxifen or anastrozole for 5 years. The study found that after 5 years, compared to women taking tamoxifen, the women taking anastrozole were 2% less likely to develop either DCIS or cancer in the same breast, cancer in the opposite breast, or distant cancer spread.  The difference was about 8% of women taking tamoxifen compared to 6% taking anastrozole.  As in the previous study, the vast majority of women survived and those taking anastrozole did not live any longer than women taking tamoxifen.2

That was a very small benefit for anastrozole compared to tamoxifen, and another study of post-menopausal women with DCIS found no difference between the two hormone treatments.3

Bottom Line:  Radiation and hormone therapy both have benefits for most women who undergo lumpectomy, because they decrease the chances of DCIS returning after surgery.  However, the benefits are quite modest and neither of these treatments affect how long women live, because almost all women diagnosed with DCIS are still alive 20 years later.

References:

  1. National Cancer Institute. Breast Cancer Treatment PDQ. (Feb. 2018). Available online: https://www.cancer.gov/types/breast/hp/breast-treatment-pdq#link/_1576_toc
  2. Margolese, Richard G et al. Anastrozole versus tamoxifen in postmenopausal women with ductal carcinoma in situ undergoing lumpectomy plus radiotherapy (NSABP B-35): a randomised, double-blind, phase 3 clinical trial.The Lancet. 2016;387(10021): 849 – 856.
  3. Forbes, John F et al. Anastrozole versus tamoxifen for the prevention of locoregional and contralateral breast cancer in postmenopausal women with locally excised ductal carcinoma in situ (IBIS-II DCIS): a double-blind, randomised controlled trial. The Lancet.2016;387(10021): 866 – 873.
  4. Cuzick, Jack et al. Effect of tamoxifen and radiotherapy in women with locally excised ductal carcinoma in situ: long-term results from the UK/ANZ DCIS trial. The Lancet Oncology. 2011; 12(1): 21 – 29