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Accelerated partial breast irradiation noninferior to whole breast irradiation for invasive breast cancer
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SAN ANTONIO — Accelerated partial breast irradiation appeared noninferior to whole breast irradiation for preventing local recurrence among women with invasive breast cancer or ductal carcinoma in situ, according to results of the RAPID trial presented at San Antonio Breast Cancer Symposium.
Accelerated partial breast irradiation was associated with less acute toxicity but an increase in late normal tissue toxicity and adverse cosmesis.
“The ipsilateral breast tumor recurrence rate was very low and absolute differences were very small during an 8-year period. Once-a-day treatment with a longer interval in between radiation fractions may not adversely affect cosmesis and is now being investigated,” Timothy J. Whelan, BSc, BM, BCh, MSc, FRCPC, associate chair of research in the department of oncology at McMaster University in Canada, said during a presentation.
Whole breast radiation is commonly used following breast-conserving surgery because it reduces the risk for local recurrence, thereby helping patients avoid mastectomy.
Accelerated partial breast irradiation is based upon the rationale that most local recurrences occur at the primary site and that a smaller volume of breast tissue can be treated in an accelerated fashion.
“Several techniques exist, many of which are resource-intensive. Three-dimensional conformal radiotherapy is an attractive approach as it is noninvasive and uses standard techniques for external beam radiotherapy that are widely available,” Whelan said.
The analysis included women (median age, 61 years) with invasive disease (82%) or ductal carcinoma in situ (18%) who underwent breast conserving surgery with clear margins of excision.
Researchers randomly assigned 1,070 patients to accelerated partial breast irradiation at a dose of 38.5 Gy in 10 fractions delivered twice daily using 3-D conformal radiotherapy or intensity-modulated radiation therapy. The other 1,065 patients underwent whole breast irradiation at a dose of 42.5 Gy in 16 daily fractions or 50 Gy in 25 daily fractions, with boost radiation when needed.
Ipsilateral breast tumor recurrence served as the primary endpoint. Secondary endpoints included DFS, EFS, OS, radiation toxicity and nurse-assessed adverse cosmesis.
During median follow-up of 8.6 years, researchers observed 65 ipsilateral breast tumor recurrences.
Researchers reported higher ipsilateral breast tumor recurrence rates in the accelerated group at 5 years (2.3% vs. 1.7%) and 8 years (3% vs 2.8%; HR = 1.27; 90% CI, 0.84-1.91).
The HR for DFS events was 1.2 (95% CI, 0.83-1.76) and the HR for EFS events was 1.16 (95% CI, 0.95-1.43).
A lower percentage of patients assigned accelerated therapy experienced acute radiation toxicity (28% vs. 45%; P < .001). However, more patients who received accelerated therapy experienced late radiation toxicity (grade 2 or higher, 32% vs. 13%; P < .001; grade 3, 4.5% vs. 1%; P < .001).
Additionally, nurse-determined adverse cosmesis rating was higher among patients who received accelerated therapy at 3 years (29% vs. 17%; P < .001) and 5 years (32% vs. 16%; P < .001). – by Jennifer Southall
Reference:
Whelan T., et al. Abstract GS4-03. Presented at: San Antonio Breast Cancer Symposium; Dec. 4-8, 2018; San Antonio.
Disclosures: Whelan reports no relevant financial disclosures. Please see the abstract for all other authors’ relevant financial disclosures.