Breast Cancer

PV QA 4 - Poster Viewing Q&A 4

TU_9_3407 - Biologic Subtypes of Primary Breast Tumors Exhibit Differences in the Radiosensitivity Index

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

Biologic Subtypes of Primary Breast Tumors Exhibit Differences in the Radiosensitivity Index
C. Liveringhouse1, K. A. Ahmed2, J. D. Purcell2, M. Mills1, G. D. Grass3, T. J. Robinson4, J. F. Torres-Roca3, and R. Diaz2; 1University of South Florida, Tampa, FL, 2H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, 3H. Lee Moffitt Cancer Center and Research Institute, Department of Radiation Oncology, Tampa, FL, 4Department of Radiation Oncology, Moffitt Cancer Center, Tampa, FL

Purpose/Objective(s): We have previously identified and validated a multigene expression index for tumor radiosensitivity called the radiosensitivity index (RSI, high index = more radioresistant). In this study, we assessed the RSI of primary breast tumor samples as a function of biologic subtype.

Materials/Methods: A total of 285 primary tumors were identified from our institution’s prospective observational tissue biorepository. Biologic subtype was determined by immunohistochemistry. Gene expression was assessed with Affymetrix Hu-RSTA-2a520709 microarray chips. The RSI 10 gene signature was calculated for each tissue sample using the previously published rank-based algorithm. RSI distributions were compared between subtypes using the Kruskal-Wallis test. Tumor and patient characteristics and clinical outcomes were assessed from review of the clinical chart.

Results: The most common histologies were infiltrating ductal carcinoma (n=235; 82%) and invasive lobular carcinoma (n=34; 12%). Median age of patients at diagnosis was 55 (range: 24-91). Tumor subtypes were luminal A (n=180; 65%), triple negative (n=46; 17%), luminal B (n=25; 9%), and HER2 (n=22; 8%). The RSIs varied significantly according to biologic subtype and in increasing order of radioresistance were HER2 (median RSI = 0.35), Luminal B (0.35), Luminal A (0.40), and triple negative (0.44; p = 0.01).

Conclusion: In this analysis assessing radiosensitivity index between primary breast tumors according to biologic subtype, significant differences were noted according to biologic subtype. Thus, biologic subtype may help inform radiotherapy decision making, especially as it pertains to dose selection.

Author Disclosure: C. Liveringhouse: None. K.A. Ahmed: None. J.D. Purcell: None. M. Mills: None. T.J. Robinson: None. J.F. Torres-Roca: Stock; Cvergenx, Inc. Patent/License Fees/Copyright; Cvergenx, Inc. Chair of Medical Advisory Board; Cvergenx, Inc. R. Diaz: Travel Expenses; AACR. Member, Advisory Council; Global Health Outreach.

Casey Liveringhouse, BA

Medical Student

Disclosure:
No relationships to disclose.

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