Comparing Three forms of Accelerated Partial Breast Irradiation

Researchers from the William Beaumont Hospital in Michigan conducted a comparative analysis of the three modalities used in accelerated partial breast irradiation (APBI) in women with early stage breast cancer and found all three methods comparable in terms of local control, survival, and cosmesis. The methods examined included interstitial brachytherapy (low and high dose), 3-D conformal external beam radiotherapy (3-D CRT), and MammoSite (MS). MammoSite is the newest of these methods, approved by the FDA in May 2002.

From 1993 to 2006, 373 patients were treated with APBI at William Beaumont Hospital; 199 had interstitial brachytherapy (120 low dose, 79 high dose), 94 had 3-D CRT, and 80 had MS. The median age of patients was 64 years. All had undergone partial mastectomy for invasive ductal carcinoma ≤ 3 cm and had up to 3 positive axillary nodes. Overall, 94% of patients had T1 tumors, 92% were axillary node negative, and 86% were estrogen-receptor (ER) positive.

Median follow-up was 6.4 years, although it was longest for the interstitial patients (10 years) and shorter for the other two modalities, at just over 4 years. Patient characteristics were well balanced between groups, although only 69% of patients receiving MammoSite had T1 tumors compared with 100% of the 3D and interstitial patients. Two-thirds of patients overall had been treated with tamoxifen; less than 20% received chemotherapy.

Peter Chen, MD (below)

William Beaumont Hospital

The 5-year actuarial local recurrence rate was 1.7% overall. Rates varied slightly among the modalities, at 1.6% for interstitial, 1.1% for 3-D CRT, and 2.6% for MammoSite (P = 0.676). According to Peter Chen, MD, associate professor, William Beaumont Hospital in Michigan, who presented the data, univariate and multivariate analyses showed the only factor significant for local recurrence was negative ER status. Median time to local recurrence was 5 years, which Dr Chen described as “somewhat late.” Overall cause specific survival was 98%, overall survival (OS) was 89%, disease-free survival (DFS) was 95%, and the rate of distant metastases was 3%.

“How do the three compare?” Dr Chen asked. “If you analyze for all the major endpoints we looked at across all there forms…for OS, cause specific survival, local recurrence, distant metastases, and DFS, there was no difference between the three.” All the patients had good cosmetic results, with 95% categorized as “good to excellent.” In the interstitial group, this increased to 99%; it was 89% for women in the 3-D CRT group and 94% for those in the MammoSite group.

“I think the Beaumont experience with these 3 forms of APBI results in comparable local control, survival, and cosmesis,” Dr Chen said. He added that additional continued follow-up was needed for the patients in the 3D-CRT and MammoSite groups to “assess the long-term efficacy and equivalence of these compared with the interstitial patients.”

The hospital plans to place all patients eligible for APBI onto protocol. “We’ll await the maturation of class I evidence from randomized trials, Dr Chen said. He noted that there are currently several phase 3 trials underway. “Off protocol , we will treat our patients based on the recently released ASTRO guidelines for suitable patients.” Abstract No. 210.