DCIS is a noninvasive form of breast cancer, and controversy has swirled over whether it represents early-stage cancer that should be treated before it becomes invasive, or if it is simply indolent disease that could be left alone or monitored. It now accounts for some 30% of cancers detected with breast screening, and some antimammography partisans have even maintained that the detection of DCIS is an example of overdiagnosis -- the detection of disease that would never harm an individual during their lifetime.
In the new study, a Canadian research team used long-term data to compare estimated deaths and actual deaths among more than 144,000 women diagnosed with DCIS between 1995 and 2014. Women with DCIS had a 3.3-fold higher risk of dying from breast cancer than someone of the same age without cancer. That risk was even higher for Black women and young women.
"This suggests that our current treatment focus on preventing invasive recurrence is insufficient to eliminate all deaths from breast cancer after DCIS," wrote the authors, led by Vasily Giannakeas, a doctoral candidate at the University of Toronto and affiliate Women's College Research Institute.
The authors used Surveillance, Epidemiology, and End Results (SEER) data of 144,524 women who underwent surgical treatment for DCIS. Patients were between the ages of 25 and 79 at diagnosis, and outcomes were tracked until death, loss to follow-up, 20 years after diagnosis, or the study cut-off date of December 31, 2016.
The authors compared the actual number of breast cancer deaths in the cohort to the expected number of deaths had the women not developed DCIS. To do so, they multiplied each woman's breast cancer incidence rates unique to her age and calendar year at diagnosis by the overall breast cancer mortality rates. The difference between the actual and expected number of deaths was presented as a standardized mortality ratio (SMR).
|Breast cancer mortality among women with DCIS by age at diagnosis
The authors estimated 459 women in the 144,524-person cohort would have died from breast cancer had they not developed DCIS. Instead, 1,540 women died from breast cancer.
This standardized mortality ratio of 3.36 suggested that women with DCIS died three times more often than would be expected given their age and year of diagnosis.
The mortality ratio also varied greatly based on patients' age and race. Women under the age of 40 died almost 12 times more frequently than those in the general population, and Black women died 7.6 times more often. The ratio was particularly grim for Black women under the age of 50, who had a SMR of 12.1.
|Breast cancer mortality among women with DCIS by race
Treatment choice also resulted in differences in the mortality ratio. Women who chose lumpectomy and radiotherapy had the best outcomes, with a SMR of 2.81. But mortality ratios were much higher for women who opted for lumpectomy alone (3.42), unilateral mastectomy (4.12), and bilateral mastectomy (4.14).
The authors cautioned that the treatment data should not be viewed in favor of lumpectomy, as women who chose to undergo mastectomy are often younger and have more extensive disease. However, it did make them question the positive long-term effects of surgery.
"To our knowledge, to date there is no empirical evidence that surgical treatment of DCIS reduces the subsequent mortality from breast cancer," they wrote. "Given the similar SMRs for women with mastectomy and those with lumpectomy, it is possible that the mortality for women who had neither form of surgical treatment would be similar to these."
The total 20-year breast cancer death rate was 3.3% for the cohort. While the authors said their study can't be used to inform treatment options, they also noted a roughly 3% death risk is too low to universally recommend chemotherapy for women with DCIS.
But some groups of women, including Black women and those under the age of 40, had death rates approaching or exceeding 10%, a level where chemotherapy may be appropriate. The authors hope future studies better clarify which patients with DCIS are at a higher risk of death in order to improve treatment options.
"The current approach is to identify women with a high risk of local recurrence and treat them with radiotherapy initially and with chemotherapy at time of invasive cancer according to the clinical profile," they wrote. Given that not all women who die of cancer following DCIS experience a local recurrence, the impact of this approach is necessarily limited."
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