CHICAGO – Radiation therapy dramatically improves local control in ductal carcinoma in situ, even in cases having favorable features, investigators reported.
The randomized Radiation Therapy Oncology Group (RTOG) 9804 trial was conducted among 585 women who had "good-risk" ductal carcinoma in situ (DCIS), meaning small, asymptomatic tumors of low grade and with adequate resection margins after lumpectomy.
Dr. Beryl McCormick
The main results showed that women had a significant 86% relative reduction in the risk of local failure if they received radiation therapy instead of observation. But the absolute 5-year rate of local failure was only about 3%, even without this intervention.
"We were able, using standard pathology methods and our Web-based RTOG pathology tool, to define good-risk or low-risk DCIS patients who had an extremely low event rate even with observation," said lead investigator Dr. Beryl McCormick at the annual meeting of the American Society of Clinical Oncology.
Nonetheless, "for this good-risk disease, the addition of radiation significantly reduced the risk of local failure. Clearly, we are expecting to follow this group out longer," added Dr. McCormick, a radiation oncologist and chief of the external beam radiotherapy service at Memorial Sloan-Kettering Cancer Center in New York.
"The study was a positive study," commented discussant Dr. Eun-Sil Shelley Hwang of Duke University Medical Center in Durham, N.C. "The reasons for that are debatable. On this analysis, there was a lower recurrence rate in the excision-only group than had been predicted, but what drove the positive findings was the much lower rate in the radiation therapy group."
Dr. Hwang speculated that the use of tamoxifen by about two-thirds of women may have contributed to the low rate of local recurrence seen even in the absence of radiation therapy.
"Further follow-up is required, because many of these patients [had] a short follow-up that may explain why we saw such low recurrence risks in this study," she proposed.
Women with DCIS who were above age 26 were eligible for RTOG 9804 if they had no symptoms (their tumors had been found mammographically or incidentally), had only low or intermediate tumor grade, had a tumor size of 2.5 cm or less, and had a resection margin width of at least 3 mm.
The 585 study participants were randomly assigned in balanced fashion to observation or radiation therapy, each with or without tamoxifen. (Overall, 62% received the drug.) Radiation therapy began within 12 weeks of final surgery, and consisted of 42.5-50.4 Gy, with no boost.
The main trial results showed that the actuarial 5-year rate of local failure (invasive or noninvasive) in the treated breast was 3.2% in the observation group and 0.4% in the radiation therapy group, corresponding to an 86% reduction in risk (hazard ratio, 0.14; P = .002), Dr. McCormick reported.
In the radiation therapy group, there were no local failures in the same quadrant as the original tumor; in contrast, in the observation group, two-thirds of the failures were in the same quadrant.
The two groups were statistically indistinguishable with respect to the rate of contralateral breast events, disease-free survival, and overall survival.
The rate of acute grade 3 or worse nonhematologic toxicities was similar in the observation group and radiation therapy group (4.0% vs. 4.2%, respectively), although lower-grade toxicities were more common in the latter. The rate of late grade 3 or worse radiation therapy toxicity was 0.7% in the group given this therapy.
Dr. McCormick disclosed no relevant conflicts of interest. Dr. Hwang disclosed that she is a consultant to Genomic Health and receives research funding from Merck and Novartis.