Dr. Hwang comments: Today, about 1/1,300 screening mammograms result in a diagnosis of DCIS. There are two important considerations when we talk about active surveillance or doing less aggressive treatment. First, what is the rate at which progression to invasive cancer can occur, either with or without treatment? Second, what is the fate of these DCIS lesions? These are issues for which we currently don’t have good answers.
We’re treating all disease detected at an early stage, and for the sake of argument, I’ll include DCIS, as if it likely will cause harm if we did absolutely nothing when, in fact, there could be many cancers that progress so slowly and have such a low propensity for developing metastatic disease that they would not likely cause any symptoms or harm during a patient’s lifetime.
Dr. Shelley E. Hwang
In autopsy series, the disease reservoir of unrecognized DCIS is about 9% and the disease reservoir of invasive cancer is about 1%. It’s not that different from prostate cancer, although at a much lower rate. These data show that there certainly are women who die with DCIS rather than of it.
We really don’t have a very solid understanding of the natural history of DCIS. If we do nothing, but maybe surgically biopsy it, what happens to these patients in the long term? In a meta-analysis, the world’s literature included only 151 cases of women who had surgical biopsy of DCIS that initially was misdiagnosed as a benign lesion and therefore didn’t undergo any further therapy, some with up to 31 years of follow-up. The long-term risk of invasive cancer in this cohort is only 22% (Breast Cancer Res. Treat. 2006;97:135-44). The annual risk of breast cancer in women with atypia is 1% per year, so this ends up looking very similar to the risk of progression that you see for atypical ductal hyperplasia or lobular carcinoma in situ.
The most common treatment for DCIS in the United States is lumpectomy with radiation. A meta-analysis by the European Breast Cancer Trialists’ Group found a 50% proportional reduction in local recurrence risk in women treated with lumpectomy and radiation vs. lumpectomy alone. The absolute magnitude of reduction was dependent on baseline recurrence risk. That’s a really important concept, because if your baseline risk is only 5%, then the 50% proportional reduction only translates into a 2.5% reduction in risk in 10 years.
The prospective, randomized Radiation Therapy Oncologists Group 9804 study randomized low-risk women with DCIS, unlike prior randomized trials that included broad eligibility criteria for DCIS. In 5 years of follow-up, the ipsilateral recurrence risk (which includes both invasive cancer and DCIS) was 3.2% in the lumpectomy-only group vs. 0.4% in the lumpectomy and radiation therapy group. The difference is highly statistically significant, however, given the small absolute difference between groups, the clinical significance certainly can be argued. There was no significant difference between groups in contralateral new primary lesions (Radiat. Oncol. 2012;84:S5).