Distortions of HER2 status designation parameters using fluorescence in situ hybridization (FISH) in breast cancer: aneusomy and proliferative rates

The accurate determination of HER2 gene amplification status by FISH is critically important in the formulation of effective treatment regimens for patients. The complex biology of cancer can complicate efforts to produce guidelines for HER2 status designation. Aneusomy in cancer and natural cell cycle processes can lead to distortions in average HER2 copy number and the HER2:CEP17 ratio used in current algorithms for HER2 amplification testing by FISH. Here, we investigate these potential sources of artificial HER2 copy number variation and their ability to alter the ultimate diagnosis in breast cancer cell lines and tumor samples. The distortive effects of aneusomy and cell cycle processes are investigated in the context of the current guidelines from the American Society of Clinical Oncologists (ASCO) and the College of American Pathologists (CAP). These guidelines vary from previous guidelines in that they attempt to infuse recent findings on the rarity of “chromosome 17 polysomy” into the guidelines by using the HER2:CEP17 ratio and the average HER2 copy number to classify cases. However, the findings on which this novel system of case grouping is predicated has not been widely-accepted, and, indeed, the evidence presented in this document contradict them. Chapter 1 explores the incongruities of the ASCO/CAP dual-probe FISH grouping system for HER2 with protein expression data in two large patient cohorts. Chapter 2 investigates aneusomy in breast cancer. Chapter 3 investigates the role of the cell cycle and proliferative rates in increasing HER2 copy number.