[109] Mutational and Clonal Intratumoral Heterogeneity of Breast Cancer

Stefanie Avril, Lyndsay N Harris, Heinz Hofler, Hannah L Gilmore. Technische Universität München, Munich, Germany; Case Western Reserve University and University Hospitals Seidman Cancer Center, Cleveland, OH; Case Western Reserve University and University Hospitals Case Medical Center, Cleveland, OH

Background: Intratumoral heterogeneity of solid tumors has long been known. However, the full spectrum of mutational heterogeneity within different areas of a single breast carcinoma has not been assessed. The aim of this study is to assess the intratumoral heterogeneity of somatic mutations at the sequence level within primary breast cancers and between axillary lymph node metastases from the same patient in order to define the extent of sampling needed to reliably represent the entire breast carcinoma.
Design: In a pilot study, 25 prospectively collected formalin-fixed and paraffin embedded samples from 6 untreated primary breast cancers (2 Luminal, 2 HER2, and 2 Basal subtypes) were analyzed. These included samples from the peripheral, intermediate and central zones of each primary tumor and several axillary lymph node metastases per patient. All samples were analyzed by targeted deep-sequencing of 40 known candidate driver mutations using miSeq Custom Amplicon technology (Illumina). The presence and frequency of mutations was compared between samples from different tumor zones and between different lymph node metastases from the same patient.
Results: We found a large variation both in the presence and frequency of 40 candidate mutations in different regions of the same primary breast carcinoma, and between different lymph node metastases from the same patient. The majority of somatic mutations were only present in some areas and not throughout the whole tumor.
Conclusions: The considerable mutational heterogeneity demonstrated in this study may lead to sampling bias when single tumor samples are used for assessing the mutational spectrum of a breast carcinoma. In addition, mutational heterogeneity may contribute to the development of resistant tumor cell clones, in particular when targeted therapies are directed against mutated oncogenes. Multiple biopsies are required to fully characterize a primary or metastatic breast cancer for the selection of targeted therapies or for prediction of treatment response. Future studies should address the question whether sequencing in greater depth of a single index lesion may in some instances replace the need for multiple tumor samples.
Category: Breast

Monday, March 4, 2013 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 15, Monday Morning

 

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