Outcomes According to Breast Cancer Subtype in Patients Treated With Accelerated Partial Breast Irradiation.
The purpose of the study was to determine outcomes for patients treated with accelerated partial breast irradiation (APBI) on the basis of breast cancer subtype (BCST).



Our single-institution, institutional review board-approved APBI database was queried for patients who had complete testing results for the estrogen (ER), progesterone (PR), and HER2/neu receptors to determine outcomes for each BCST. Women were assigned as luminal A (LA), luminal B (LB), HER2, and basal BCST using their ER, PR, and HER2/neu receptor status. Degree of ER expression supplemented the receptor-based luminal BCST assignment. Two hundred seventy-eight patients had results for all 3 receptors (LA = 164 [59%], LB = 81 [29%], HER2 = 5 [2%], basal = 28 [10%]), which were submitted for analysis (ipsilateral breast tumor recurrence [IBTR], regional nodal failure, distant metastasis [DM], disease-free survival [DFS], cause-specific survival [CSS], and overall survival [OS]).



Median follow-up was 5.4 years (range, 0.1-12.4 years). Basal and HER2 subtype patients had higher histologic grades (Grade 3 = 75% vs. 10% LA/LB; P < .001), larger tumors (13.0 mm basal vs. 10.7 mm LA/LB; P = .059), and were more likely to receive chemotherapy (68% vs. 15% LA/LB; P < .001). Margin and nodal status were similar among BCSTs. At 5 years, IBTR rates were similar (1.8%, 2.9%, 0%, and 4.8%) for LA, LB, HER2, and basal subtypes, respectively (P = .62). DM was only seen in LA (2.9%) and LB (1.3%) (P = .83). DFS (95%-100%), CSS (97%-100%), and OS (80%-100%) were not statistically different (P = .97, .87, .46, respectively).



Five-year local control rates after breast-conserving surgery, APBI, and appropriate systemic therapy are excellent for luminal, HER2, and basal phenotypes of early-stage breast cancer; however, further study of receptor subtype effect on risk stratification in early-stage breast cancer is needed.
Department of Radiation Oncology, Willis-Knighton Health System, Louisiana State University Health Sciences Center, Shreveport, LA. Electronic address: j.ben.wilkinson@gmail.com.
J Ben
JB
Wilkinson
Department of Radiation Oncology, Beaumont Cancer Institute, Oakland University William Beaumont School of Medicine, Royal Oak, MI.
Chirag
C
Shah
Department of Pathology, Beaumont Cancer Institute, Oakland University William Beaumont School of Medicine, Royal Oak, MI.
Mitual
M
Amin
Department of Medical Oncology, Beaumont Cancer Institute, Oakland University William Beaumont School of Medicine, Royal Oak, MI.
Laura
L
Nadeau
Department of Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX.
Simona F
SF
Shaitelman
Department of Radiation Oncology, Beaumont Cancer Institute, Oakland University William Beaumont School of Medicine, Royal Oak, MI.
Peter Y
PY
Chen
Department of Radiation Oncology, Beaumont Cancer Institute, Oakland University William Beaumont School of Medicine, Royal Oak, MI.
Inga S
IS
Grills
Department of Radiation Oncology, Michigan Healthcare Professionals, 21st Century Oncology, Farmington Hills, MI.
Alvaro A
AA
Martinez
Department of Radiation Oncology, Beaumont Cancer Institute, Oakland University William Beaumont School of Medicine, Royal Oak, MI.
Christina K
CK
Mitchell
Department of Radiation Oncology, Beaumont Cancer Institute, Oakland University William Beaumont School of Medicine, Royal Oak, MI.
Michelle F
MF
Wallace
Department of Radiation Oncology, Michigan Healthcare Professionals, 21st Century Oncology, Farmington Hills, MI.
Frank A
FA
Vicini
D014408:Biomarkers, Tumor / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology* / Q000532:radiotherapy*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D060787:Neoplasm Grading; D009367:Neoplasm Staging; D011379:Prognosis; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D015996:Survival Rate; D047368:Tumor Burden
D014408:Biomarkers, Tumor; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C508053:ERBB2 protein, human
APBI; Brachytherapy; Breast cancer subtype; Radiotherapy; Triple negative