Interphase FISH for Residual Disease: Proposal for a Qualitative Determination of Rare Events

Interphase fluorescence in situ hybridization (FISH) cutoff values are calculated using various mathematical methods to determine whether abnormalities seen are at reportable (statistically significant) levels. However, for interphase FISH studies of samples obtained from oncology patients who have been transplanted or treated, these cutoff values may result in reporting a false negative result due to the small percentage of residual disease that falls below such a cutoff value. Failure to detect the rare abnormal cells may impact patient care and prognosis. For such situations, the two questions are: is the disease still present, and if so, how prevalent is it? The first question is qualitative and the second is quantitative. Traditionally, only the quantitative parameters have been used for determining reportability. Here we propose a method to account for both qualitative and quantitative evaluations of interphase FISH results.