Fluorescence In Situ Hybridization for TP63 Rearrangements in T‐cell Lymphomas: Single Site Experience of 470 Patients and Implications for Clinical Testing

AIMS: The aims of this study were to review our 5-year experience with clinical FISH testing for TP63 rearrangements using both TP63 break-apart (BAP) and TBL1XR1/TP63 dual-fusion (D-FISH) probes to evaluate the frequency of TP63 rearrangements and the distribution of TBL1XR1 vs. alternate partner loci, and to assess whether both probe sets are necessary in all cases undergoing FISH testing. METHODS AND RESULTS: A retrospective review of the Mayo Clinic cytogenetic database identified 470 patients evaluated by FISH testing for TP63 rearrangements in formalin-fixed paraffin-embedded (FFPE) tissue using both BAP and D-FISH probes. Of these, 25 (5.3%) had TP63 rearrangements. All samples were being investigated for anaplastic large-cell lymphoma or other T cell lymphoma subtypes. A TBL1XR1 partner was identified by D-FISH in 12 (48%) of 25 cases. All cases positive by TBL1XR1/TP63 D-FISH were also positive by TP63 BAP FISH. CONCLUSION: This is the largest series of TP63 rearrangements to date. The frequency of positive results among cases referred to a large reference laboratory for TP63 FISH testing was 5.3%. Approximately half of TP63 rearrangements have a TBL1XR1 partner. TP63 BAP FISH testing is sufficient for up-front testing of FFPE tissue samples. However, because of the genomic proximity of the TP63 and TBL1XR1 loci, we recommend reflex TBL1XR1/TP63 D-FISH testing in positive and equivocal cases.