San Antonio, October 21, 2018 — Whole breast radiation (WBRT) significantly reduced local recurrence in women with “good risk” (low risk) ductal carcinoma in situ (DCIS) following breast conservation surgery, according to researchers from Memorial Sloan Kettering Cancer Center (MSK), who presented this data in a press conference at the annual meeting of the American Society for Radiation Oncology (ASTRO). Researchers found that the 12-year cumulative incidence of local recurrence was 2.8 percent with whole breast radiation, compared to 11.4 percent with observation. More specifically, the 12-year cumulative incidence of invasive local recurrence was 1.5 percent for those in the WBRT arm and 5.8 percent for those who did not receive radiation.
“We were surprised that the effect that WBRT had on local recurrence in this specific population was larger than expected,” said Beryl McCormick, MD, Chief of the External Beam Radiotherapy Service at MSK and lead investigator of the NRG Oncology/RTOG multicenter trial. “These findings — from the only prospective, randomized trial to assess the impact of whole breast radiation versus observation in women with ‘good risk’ DCIS — should inform a meaningful patient-physician discussion about risks, benefits, and the individual’s own degree of comfort,”
The initial results of this trial, including seven years of follow-up, were reported in 2013 and published in the Journal of Clinical Oncology in 2015. From 1999 to 2006, 636 individuals were randomly assigned to WBRT with standard doses or to an observation arm. “Good risk” DCIS was defined for this trial as clinically occult DCIS, found by a mammogram or an incidental finding at surgery, that was greater than or equal to 2.5 centimeters (cm) in size, with final margins less than or equal to 3 millimeters, and having a low or intermediate nuclear grade. The new analyses include follow-up data for 629 people whose median age was 58 years. Mean pathological tumor size was 0.60 cm, with 61 percent less than or equal to 0.5 cm and 65 percent with either a margin width greater than or equal to 1 cm or a completely negative re-excision specimen. The highest nuclear grade was one in 44 percent of participants and two in 56 percent. For both treatment arms, 69 percent of people planned use tamoxifen (Nolvadex®), which was optional. However, only 58 percent of those who had WBRT and 65 percent of those in the observation arm used it (p=0.05).
Median follow-up time was 12.4 years. After 12 years, the cumulative incidence (CI) of local recurrence was 2.8 percent (95 percent CI: 1.1, 5.6) for those in the WBRT arm and 11.4 percent (7.7, 15.8) for those in the observation arm (p=0.0001; HR=0.26, 95 percent CI: 0.13, 0.54). The 12-year cumulative incidence of invasive local recurrence was 1.5 percent (0.4, 4.0) for those in the WBRT arm and 5.8 percent (3.2, 9.5) for those who did not receive radiation (p=0.016; HR=0.34, 95 percent CI: 0.14, 0.85). In multivariate analysis, only those who received both WBRT (p=0.0003; HR=0.25, 95 percent CI: 0.12, 0.53) and tamoxifen (p=0.024; HR=0.50, 95 percent CI: 0.27, 0.91) experienced reduced local recurrence. Neither age nor pathological tumor size were significant for predicting local recurrence or invasive local recurrence. There were no significant differences between the treatment arms for overall survival, disease-free survival, or mastectomy use.
“While DCIS is a very early form of breast cancer with typically low rates of recurrence, not all cases are the same and every individual may have a different definition of what poses a substantial risk to them. Now that we have identified the specific risks of recurrence in this low-risk population, individuals undergoing treatment can benefit from more personalized treatment plans,” explained Dr. McCormick.
This project was supported by grants U10CA180868 (NRG Oncology Operations), U10CA180822 (NRG Oncology SDMC), and UG1CA189867 (Community Oncology Research Program, or NCORP) from the National Cancer Institute.