Ductal carcinoma in situ (DCIS) is a type of non-invasive breast cancer in which breast cancer cells are confined to the milk ducts and have not spread beyond their walls to invade surrounding tissues. Even when treated, approximately 15% of women with DCIS are eventually diagnosed with invasive breast cancer. DCIS can be eliminated with mastectomy, but this is normally considered overtreatment for a condition that in itself is not life threatening and might not progress to invasive breast cancer.

Radiation treatment should follow breast conserving surgery for DCIS

Progression of DCIS to invasive breast cancer is more likely if radiotherapy is omitted after lumpectomy or other breast-conserving surgery. Radiation reduces both the risk of recurrence of DCIS and the risk of progression to invasive breast cancer. Radiation appears to have an ongoing protective effect against DCIS recurrence, but protects against invasive disease only during the first five years after treatment. Efforts to identify women who can safely treated for DCIS with surgery alone have not been satisfactory—some women with small DCIS tumors and generally favorable characteristics will still experience a recurrence.

Some women may be inclined to reject radiation because of its known side effects, including heart damage. However, care can (and should) be taken to minimize this risk. The risk of recurrence in most cases will outweigh that of potential heart damage, although this should be assessed on an individual basis. Now a large new study has reported that more than one fifth of cases of DCIS recurrence or progression to invasive breast cancer could be prevented if all women with DCIS who receive breast conserving surgery also undergo radiation treatment.

Latest research affirms the importance of radiotherapy

The Canadian study referenced at the beginning of this news story was designed to evaluate the effectiveness of breast-conserving surgery for DCIS, alone or with radiation treatment. Despite the evidence for its efficacy, half of women do not receive radiotherapy after breast-conserving surgery for DCIS. The study included all 3,762 women diagnosed with DCIS and treated with breast-conserving surgery in Ontario between 1994 and 2003. A total of 1,895 (50.4%) of the women received radiation treatment. Medical chart reviews were used to validate treatments and outcomes. The women were followed for a median of 10 years.

Recurrences (either recurrence of DCIS or progression to invasive breast cancer) occurred in 363 (19.4%) of the women who did not receive radiation treatment compared to 233 (12.3%) of those who did. The 10-year estimated DCIS recurrence rates for women who did not and did receive radiotherapy were 10.8% and 6.1%. The comparable 10-year estimated invasive breast cancer rates were 10.0% and 7.0%. The authors estimate that 22% of the recurrences in Ontario women treated for DCIS between 1994 and 2003 would have been prevented if all of the women had received radiation treatment. In other words, omission of radiotherapy after breast-conserving surgery for DCIS resulted in significant numbers of recurrences that could have been avoided. The authors comment that additional markers are needed to identify low risk women in whom radiation can safely be omitted.

Please see our article on what happens after treatment for DCIS for more information.