SAN FRANCISCOA new analysis based on SEER data shows a very low probability of fatal breast cancer among women with DCIS for up to 10 years after diagnosis and treatment. Further, the data suggest that women with DCIS are, overall, healthier than the general population, Virginia L. Ernster, PhD, reported at a poster session of the San Antonio Breast Cancer Symposium.
The findings came from an analysis of 12,946 DCIS cases in the NCI's Surveillance Epidemiology and End Results (SEER) data base. The cases were diagnosed between 1978 and 1992, and all the women were at least 40 years old at the time of diagnosis. Virtually all the cases were treated surgically. Follow-up ranged from one to 16 years (average, 46 months).
Overall, 1,148 women had died since their DCIS diagnosis. Breast cancer accounted for 134 deaths, or 1.04% of the DCIS population, whereas 7.9% of women diagnosed with localized invasive breast cancer during the same period died of their cancer, said Dr. Ernster, professor of epidemiology and biostatistics, University of California, San Francisco. Among women with DCIS followed for 10 years, 2.6% died of breast cancer.
Dr. Ernster and her colleagues used a standard mortality ratio (SMR), which, in this case, is the ratio of observed deaths among women with DCIS to expected deaths based on the experience of women in the general population. The analysis showed a higher relative breast cancer mortality among DCIS patients diagnosed between 1978 and 1983 (SMR of 3.16) than in those diagnosed and treated since 1984 (SMR of 1.5).
DCIS also was associated with a lower cardiovascular mortality than the general population. For women diagnosed with DCIS from 1978 to 1983, the SMR for cardiovascular disease death within five years of their DCIS diagnosis was 0.86, and for women diagnosed after 1983, the SMR was 0.62.
All-cause mortality was lower for the DCIS cohort than for women in the general population after five years (SMR, 0.83 versus 1.00) but was virtually identical after 10 years.
The results suggest that women with DCIS represent a healthy segment of the population, that they live healthier lifestyles, and that they have more regular medical checkups, Dr. Ernster said.
However, she cautioned that a number of studies have suggested that not all DCIS is alike. Some forms of the cancer appear to be more aggressive and more likely to develop into invasive breast cancer.
"Because almost all women with DCIS were treated surgically, it is impossible to tell from these data whether their very low risk of breast cancer death means that the disease is relatively benign or that the therapy is effective," she said. "We need longer follow-up to adequately assess that issue."