False positivity of ETV6/RUNX1 detected by FISH in healthy newborns and adults

The leukemia-associated ETV6-RUNX1-translocation frequently emerges prenatally. Reverse-transcriptase PCR screening may indicate presence of ETV6-RUNX1 transcripts in random cord blood samples. Subsequent cell enrichment validation finds significantly lower levels than validation applying fluorescence in situ hybridization (FISH) (<10(-5) vs. 10(-3) to 10(-4)). Using three FISH probe sets, we screened 179,000 cells from ETV6-RUNX1-positive dilution series, healthy adults and random cord blood samples. The t(12;21) single fusion extra signal translocation probe and the ETV6 break apart probe gave false positive results mimicking ETV6-RUNX1-positive cell levels of 10(-3). This questions the paradigm that 1% of newborns have ETV6-RUNX1-positive cells at levels of 10(-3) to 10(-4).