A Novel Break Apart Fluorescence In Situ Hybridization Probe Using an Extra Signal Strategy Shows Superior Sensitivity and Specificity in Detecting MYC Translocations.
Mark E Law, Ellen D McPhail. Mayo Clinic, Rochester, MN; Mayo Clinic, Rochester
Background: The identification of MYC translocations is important for the classification and management of lymphomas. Interphase fluorescence in situ hybridization (FISH) using breakapart (BAP) probes is widely used to determine the presence or absence of this translocation. Presently available commercial MYC BAP probes are prone to either false negative results due to lack of coverage for minor breakpoints (BVR2 breakpoint cluster region; Dako [DK]), or false positive results due to the presence of a large gap (1.6MB; Abbott Molecular [AM]). To overcome these limitations, we developed a MYC BAP probe ((homebrew [HB]) with a small gap (181kB) and a large distal region that spans the minor breakpoint region.
Design: In order to evaluate the sensitivity and specificity of these 3 MYC BAP probes (DK, AM and HB), interphase FISH was performed using each probe on formalin fixed paraffin embedded (FFPE) sections of 1 normal tonsil (negative control), Raji cell line (positive control), and 6 B-cell lymphomas whose MYC translocation status had been previously determined using the AM probe in our clinical practice. We used 3 lymphoma cases lacking a MYC translocation, 1 possessing a typical MYC translocation involving the major breakpoint region, and 2 possessing MYC translocations involving different minor breakpoint regions. Signals that were not overlapped or touching were categorized as translocated.
Results: Using this scoring method normal tonsil showed no split signals using the DK and HB probes, while 25/500 (5%) showed a split signal (false positive) using the AM probe. The lymphomas without a translocation and the lymphoma with a typical translocation were correctly analyzed using all 3 probe sets. Both lymphomas with MYC translocations involving the minor breakpoint region were positive using the AM and HB probe sets, while 1 case (which possessed the more distal breakpoint) was negative using the DK probe.
Conclusions: The homebrew MYC BAP FISH probe showed superior specificity to the AM probe and superior sensitivity to the DK probe. It is easy to score and is amenable to routine clinical use. The strategy of designing a BAP probe with a small gap to minimize false positive results and a large flanking probe to minimize false negative results may be applicable for detecting other translocations with varying breakpoints.
Monday, February 28, 2011 1:00 PM
Poster Session II # 262, Monday Afternoon