Radiation Therapy Cuts Recurrence in 'Good Risk' DCIS

Roxanne Nelson, BSN, RN

October 22, 2018

Patients with low-risk ductal carcinoma in situ (DCIS) are unlikely to experience disease recurrence following breast conservation surgery, but radiation therapy can reduce that small risk even further.

New findings presented at the American Society for Radiation Oncology (ASTRO) 2018 showed that whole-breast radiation therapy (WBRT) reduced recurrence by half compared to observation. The reduction in recurrence rate was much larger than the study authors had anticipated.

"The larger than expected reduction has yielded meaningful results despite not meeting original targeted accrual," explained lead author Beryl McCormick, MD, FASTRO, chief of the External Beam Radiotherapy Service at Memorial Sloan Kettering Cancer Center and professor of radiation oncology at Cornell University in New York City.

The study included 629 patients, with a median follow-up of 12.4 years. The cumulative incidence of local recurrence was 2.8% in the WBRT arm vs 11.4 % in the observation arm (hazard ratio [HR], 0.26; P = .0001). The cumulative incidence of invasive local recurrence was 1.5% in the WBRT arm vs 5.8 for the conservation arm (HR, 0.34; P = 016).

The study is the first to investigate postsurgery radiation therapy exclusively among women with low-risk disease.

"Findings should inform meaningful patient-doctor discussions about risks, benefits, and the patient's own degree of comfort — which varies greatly — with regard to local control with or without radiation," said McCormick.

DCIS is considered to be a preinvasive or precancerous lesion that does not metastasize to other parts of the body. Prior to the advent of screening mammography, DCIS was rarely diagnosed. There has been discussion as to how aggressively DCIS should be treated.

A recent study using data from the SEER database from 1998 to 2014 found that lumpectomy plus radiation therapy was associated with a statistically significant reduction in risk for breast cancer–related death compared with either lumpectomy or mastectomy alone in women with DCIS. However, the clinical benefit is small, and routine radiation therapy is not advised.

Good Risk Disease Can Benefit

Although DCIS is generally noninvasive, it has been unclear which cases are most likely to progress.

"DCIS used to be considered one entity, and we were convinced that all DCIS are not all alike," said McCormick. "And we were the first to define 'good risk' and 'high risk,' " she said.

The current study, she added, was designed to assess whether radiation therapy would reduce the risk for local failure only in patients at with good-risk or low-risk DCIS.

In this study, the authors evaluated the impact of WBRT in comparison with observation in women with good-risk DCIS following breast conservation surgery. For this trial, good-risk DCIS was defined as clinically occult DCIS that was detected either through mammography or incidentally. Furthermore, the tumor had to be 2.5 cm or smaller; margins had to be 3 mm or less; and the tumor had to be of low or intermediate nuclear grade.

The women in the cohort were randomly assigned to either WBRT with standard doses or to observation. The use of tamoxifen for 5 years was optional. Randomization took place from 1999 to 2006; 7-year interim results were reported in 2015.

In the current, updated analysis, 76% of the participants were postmenopausal. Pathologic tumor size was 0.60 cm; 61% of the tumors were 0.5 cm or smaller; and for 65% of cases, tumor margin width was 1.0 cm or larger or a re-excision specimen was completely negative for disease. Grade 1 tumors were detected in 44% of the group; grade 2 tumors were diagnosed in the remaining 56%. Tamoxifen was used by 58% of patients in the WBRT arm and by 65% in the observation arm (P = .05).

Upon multivariate analysis, only WBRT (HR, 0.25; P = .0003) and treatment with tamoxifen (HR, 0.50; 95% CI, 0.27 - 0.91; P = .024) were associated with reduced local recurrence. Factors such as age (<50 years vs ≥50 years) and pathologic tumor size were not significant for predicting local recurrence or invasive local recurrence. As expected, there were no significant differences between the two groups with respect to overall survival, disease-free survival, or treatment with mastectomy.

Helpful for Guiding Decisions

Sheryl Green, MD, associate professor of radiation oncology at Mount Sinai Health System, New York City, noted that these results are very useful for guiding decision making for women with good-risk DCIS.

The risk of a recurrence appears to increase over time. Dr Sheryl Green

"Long-term follow-up continued to demonstrate a benefit to radiation treatment in preventing recurrences, both of DCIS and breast cancers," she said. "The risk of a recurrence appears to increase over time, reaching 12% at 12 years, and this is particularly meaningful in decision making for younger women and women with longer life expectancies."

Green added that for "these women who elect to forgo radiation treatment, the study confirmed that women were able to be treated at the time of recurrence without compromising their survival."

The study was funded by the National Cancer Institute. Dr McCormick and Dr Green have disclosed no relevant financial relationships.

American Society for Radiation Oncology (ASTRO) 2018. Abstract LBA 1, presented October 21, 2018.

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