External beam accelerated partial-breast irradiation using 32 gy in 8 twice-daily fractions: 5-year results of a prospective study.
OBJECTIVE
External beam accelerated partial breast irradiation (APBI) is an increasingly popular technique for treatment of patients with early stage breast cancer following breast-conserving surgery. Here we present 5-year results of a prospective trial.


METHODS
From October 2003 through November 2005, 98 evaluable patients with stage I breast cancer were enrolled in the first dose step (32 Gy delivered in 8 twice-daily fractions) of a prospective, multi-institutional, dose escalation clinical trial of 3-dimensional conformal external beam APBI (3D-APBI). Median age was 61 years; median tumor size was 0.8 cm; 89% of tumors were estrogen receptor positive; 10% had a triple-negative phenotype; and 1% had a HER-2-positive subtype. Median follow-up was 71 months (range, 2-88 months; interquartile range, 64-75 months).


RESULTS
Five patients developed ipsilateral breast tumor recurrence (IBTR), for a 5-year actuarial IBTR rate of 5% (95% confidence interval [CI], 1%-10%). Three of these cases occurred in patients with triple-negative disease and 2 in non-triple-negative patients, for 5-year actuarial IBTR rates of 33% (95% CI, 0%-57%) and 2% (95% CI, 0%-6%; P<.0001), respectively. On multivariable analysis, triple-negative phenotype was the only predictor of IBTR, with borderline statistical significance after adjusting for tumor grade (P=.0537).


CONCLUSIONS
Overall outcomes were excellent, particularly for patients with estrogen receptor-positive disease. Patients in this study with triple-negative breast cancer had a significantly higher IBTR rate than patients with other receptor phenotypes when treated with 3D-APBI. Larger, prospective 3D-APBI clinical trials should continue to evaluate the effect of hormone receptor phenotype on IBTR rates.
Harvard Radiation Oncology Program, Boston, Massachusetts, USA. ataghian@partners.org
Itai M
IM
Pashtan
Abram
A
Recht
Marek
M
Ancukiewicz
Elena
E
Brachtel
Rita F
RF
Abi-Raad
Helen A
HA
D'Alessandro
Antonin
A
Levy
Jennifer Y
JY
Wo
Ariel E
AE
Hirsch
Lisa A
LA
Kachnic
Saveli
S
Goldberg
Michelle
M
Specht
Michelle
M
Gadd
Barbara L
BL
Smith
Simon N
SN
Powell
Alphonse G
AG
Taghian
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000737:chemistry / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D018270:Carcinoma, Ductal, Breast / Q000737:chemistry / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D015412:Mastectomy, Segmental; D008875:Middle Aged; D016609:Neoplasms, Second Primary / Q000473:pathology; D011446:Prospective Studies; D020266:Radiotherapy, Conformal / Q000379:methods*; D047368:Tumor Burden