Bizuayehu Tesfaye / AP Images
Most of these Stage 0 cancers are discovered with mammogram screenings.
After the discovery of this condition - ductal carcinoma in situ (DCIS) - the vast majority of women undergo a surgical procedure: either a lumpectomy, a lump removed from their breast, or a mastectomy or double mastectomy, removing one or both breasts.
A major new study published August 20 in JAMA Oncology calls the effectiveness and necessity of those treatment strategies into question, finding that for the majority of patients, these aggressive treatments don't prevent women from dying of breast cancer.
Approximately 20% of breast cancers detected by mammograms are DCIS cases. As an accompanying editorial in JAMA notes, we now find and treat these DCIS cases because of screening.
Before regular screening began, these cases made up just 3% of breast cancers. We find and treat these cases now because there's a general belief that - even though they aren't usually thought of as potentially fatal themselves - DCIS is a precursor to future invasive cancer. But as Dr. Laura Esserman and Dr. Christina Yau note in the editorial, finding and treating tens of thousands more DCIS lesions each year hasn't reduced the overall number of invasive breast cancers.
If DCIS is really a precursor, finding and treating it more frequently should lower those numbers.
How we treat Stage 0 breast cancer now
The authors of the JAMA study looked at 108,196 women who received a DCIS diagnosis between 1988 and 2011. According to their calculations, a woman who receives a diagnosis of this Stage 0 cancer has about a 3.3% chance of dying of that cancer within 20 years.
They write that this is 1.8 times higher than the general population's risk of dying from breast cancer in that same period, but still a low mortality rate overall. Certain sub-groups were much more likely to die of breast cancer after a DCIS diagnosis: women under 35 and black women, for example. But as the accompanying editorial notes, for most patients, the likelihood of dying within 20 years is relatively similar to the likelihood that any woman will die of breast cancer during her lifetime, which the American Cancer Society says is a 3% chance.
Approximately half of the women in the study had a lump removed, and almost all the rest had either a mastectomy or double mastectomy.
The authors say that while removing a lump or a breast may have prevented another invasive cancer from showing up in the breast, it did not prevent death from breast cancer, which - much to their surprise - can apparently spread in rare cases even before the DCIS is detected and removed. The majority of (the small percentage) of women who died of breast cancer in the study group didn't ever have another invasive cancer in their breast, but died of the disease anyway.
In other words, for most women, DCIS may be less dangerous than we thought and doesn't necessarily need to be removed; that would help explain why aggressive treatment has not reduced the number of invasive breast cancers found overall. In the small number for whom DCIS is more dangerous than previously believed, meanwhile, current approaches to screening and treatment may be inadequate.
Rethinking treatment
We may be fundamentally misunderstanding what a DCIS diagnosis means and how to treat it, the results suggest. "Stage 0 cancer" may not be a precursor after all, but instead could be either a risky cancer in itself or essentially harmless, depending on other risk factors - but treating it as a "precancer" may not be effective.
REUTERS/Edgard Garrido
A volunteer makes a breast prosthesis for mastectomy bras.
For most patients, especially older women, the chances of dying from breast cancer after a DCIS diagnosis were low in the first place.
This brings the lead author of the study, Dr. Steven Narod, to a strategy that many might find surprising. "I think the best way to treat DCIS is to do nothing," he told the New York Times. Cancer treatments, especially invasive surgical procedures, come with their own risks and side effects. For the lower-risk DCIS cases, he argues that it may be better not to rush into any treatment. Narod did tell the CBC that it's possible some of those surgeries have been effective, though - observations of women who have foregone treatment would be necessary to know for sure.
Other experts told the Times that it was too soon to change treatment strategies, but that this study should be an impetus to look at new treatment approaches. The chief medical officer at the American Cancer Society, Dr. Otis Brawley, told the Times that it looks like we've been "too enthusiastic" in treating DCIS, but that now there should be a clinical trial that compares various treatments to receiving no treatment.
In the JAMA editorial, Esserman and Yau say we should rethink what DCIS means in the first place, by looking at the risk factors of the patient and the particular molecular components of the cancer. For high risk patients - women under 35, black women, and DCIS cases with certain molecular signatures - they still recommend aggressive treatment.
Those are the cases where DCIS is most likely to lead to death, and they argue that those cases may be fundamentally different from other Stage 0 cancer cases.
In the other non-high-risk cases, they write that this study is a good reason to try other types of treatments that may have fewer side effects, like hormonal treatments or behavioral changes.
"As we learn more," Esserman told the Times, "that gives us the courage to try something different."