Ductal carcinoma in situ (DCIS, or stage 0 breast cancer) accounts for approximately 20% of breast cancers detected by a mammogram. A new study has found that chances of dying from these very early breast cancer are small, but the disease is riskier for young women and blacks; in addition, it reported the same disparities seen for more advanced cancer. The findings are likely to fuel the debate regarding how to treat these early cancers that some scientists have said should not even be considered a true cancer because they rarely spread. The findings were published online on August 20 in the journal JAMA Oncology by researchers at Women’s College Research Institute, Women’s College Hospital, Toronto, Ontario, Canada; and Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
The study authors note that women with ductal carcinoma in situ often develop a second primary breast cancer, and some ultimately die of breast cancer; 5% of cases are diagnosed in women under the age of 40 years. It is unclear what factors predict mortality after a diagnosis of DCIS, and of importance, the impact of patient characteristics, such as age at diagnosis and ethnic group, on breast cancer mortality has not been studied. Therefore, the researchers conducted a study to estimate the 10- and 20-year mortality from breast cancer following a diagnosis of DCIS and to determine whether the mortality rate is influenced by age at diagnosis, ethnicity, and initial treatment received.
The researchers reviewed data from the Surveillance, Epidemiology, and End Results (SEER) 18 registries database. They extracted data on women who received a diagnosis of DCIS from 1988 to 2011 (108,196 women). They reviewed age at diagnosis, race/ethnicity, pathologic features, date of second primary breast cancer, cause of death, and survival. The women’s risk of dying of breast cancer was compared to that of women in the general population. Statistical analysis was conducted to estimate the increased risk by age at diagnosis, clinical features, ethnicity, and treatment.
The investigators found that among the women with DCIS, the average age at diagnosis of DCIS was 53.8 (range: 15-69) years and the average duration of follow-up was 7.5 (range: 0-23.9) years. At 20 years, the breast cancer–specific mortality was 3.3% overall and was higher for women who received a diagnosis before age 35 years compared to older women (7.8% vs. 3.2%; 2.58-fold increased risk). It was also higher for blacks compared to non-Hispanic whites (7.0% vs. 3.0%; 2.55-fold increased risk). The risk of dying of breast cancer increased after developing an invasive breast cancer in the same breast (18.1-fold increased risk). A total of 517 women died of breast cancer following a DCIS diagnosis (average follow-up, 7.5 years; range, 0-23.9 years) without experiencing an in-breast invasive cancer prior to death. Among patients who received a lumpectomy, radiotherapy was associated with a reduction in the risk of an invasive recurrence at 10 years in the same breast (2.5% vs. 4.9%; 0.47-fold decreased risk but not of breast cancer–specific mortality at 10 years (0.8% vs. 0.9%; 0.86-fold decreased risk).
The authors concluded that important risk factors for death from breast cancer following a DCIS diagnosis include age at diagnosis and black ethnicity. In addition, the risk of death increases after a diagnosis of a second primary invasive breast cancer in the same breast; however, prevention of these recurrences by radiotherapy does not decrease breast cancer mortality at 10 years.