The American Society of Therapeutic Radiology and Oncology (ASTRO) consensus panel guidelines for the application of accelerated partial breast irradiation (APBI), deeming some women “unsuitable,” does not differentiate a subset of patients with a significantly worse rate of ipsilateral breast tumor recurrence (IBTR) when treated with the MammoSite breast brachytherapy catheter to deliver APBI, said Peter Beitsch, MD, of Dallas Surgical Group in Dallas.
During a press conference at the 11th annual meeting of the American Society of Breast Surgeons (ASBS) in Las Vegas on April 30, Beitsch presented his study which applied the ASTRO guidelines for APBI to patients treated with this technique on the ASBS MammoSite registry trial to determine potential differences in outcome of patients classified in the “unsuitable” category.
Beitsch explained that the guidelines-released in the fall of 2009- classified women into three groups. “[The classifications are] literature based-or lack thereof, and they gave them what I believe is the unfortunate names of “suitable,” “cautionary” and “unsuitable.” Unsuitable meaning not enough scientific evidence to allow [ASTRO] to say they were good candidates or not, but they chose the title “unsuitable”--their word, not my word,” he noted.
In 97 institutions, the researchers observed that of the 1,449 cases treated with APBI on the registry trial, 176 fit the criteria for the “unsuitable” panel's category. Beitsch explained that this category typically consists of younger women, usually less that 50 years old presenting with tumors greater than three centimeters, and/or positive lymph nodes.
Of the 176 cases, 130 of the women were less than 50 years old, and 13 had positive margins, 38 had positive lymph nodes, six had tumors greater than three centimeters in size and 11 had an epidermal inclusion cyst greater than three centimeters. Median follow up was 49.2 months and IBTR and regional nodal failure rates were assessed, they wrote.
According to Beitsch and colleagues, the five-year actuarial rate of IBTR for “unsuitable” cases was 5.28 percent and the regional nodal failure rate was .63 percent. In comparison to both the suitable and cautionary groups (1,273 cases), the five-year actuarial IBTR rates were 3.62 percent. For invasive-only (1,255 cases), 3.88 percent and for invasive only, excluding unsuitable invasive cases (1,105 cases), 3.91 percent.
The researchers wrote: “On univariate analysis for variables potentially associated with IBTR in all 1,255 cases with invasive cancer (including age, tumor size, nodal status, overall stage, margin status, ER status, presence of an EIC, and ASTRO unsuitable category designation), only negative ER status was associated with the five-yr rate of IBTR. No other variable (including unsuitable designation by the ASTRO guidelines) was associated with a higher rate of IBTR.”
Beitch noted that the study found that patients who were classified as “unsuitable” for APBI by ASTRO presented “excellent or comparable” results compared to whole breast irradiation. In addition, “In the MammoSite registry, patients who were categorized as 'unsuitable' by ASTRO showed no higher risk or local, regional or even distant failure,” he offered.
“We believe the ASTRO guidelines should be used cautiously until more data is available to validate them and should not be used to exclude women for this treatment,” concluded Beitch.