Newly designed breakapart FISH probe helps to identify cases with true MECOM rearrangement in myeloid malignancies.

A home-brew, tri-color MECOM breakapart FISH probe with a full MECOM coverage labeled with a separate dye is compared in parallel with a 2-color commercial MECOM breakapart probe in 17 cases of hematologic malignancies. Cases with a typical positive signal pattern (or "balanced" signal pattern) (n = 2) and a negative result (n = 3) using the commercial probe achieved the same results using the new probe (100% concordance), whereas 9 of 12 (75%) remaining cases with an atypical signal pattern (or "unbalanced" signal pattern) using the commercial probe showed a "balanced" signal pattern using the new probe. Three cases with undetermined MECOM rearrangement status by the commercial probe were further clarified with no MECOM rearrangement in 2 cases and presence of a subclone with simultaneous gain and rearrangement of MECOM in 1 case. More importantly, the new probe is capable of determining the presence, location and integrity of MECOM after rearrangement. In conclusion, atypical signal patterns obtained using a commercial FISH probe for MECOM can be solved through re-design and optimization of a new BAP probe, especially in those cases with a true MECOM rearrangement. The potential of the new probe for use in the clinical laboratory will be further investigated. (Word count: 196).