The A20 (also called TNFAIP3)/PRDM1/SHGC-79576 DNA-FISH Probe is designed to detect dele­tion of the A20 gene located on 6q23 and the PRDM1 gene located on 6q21 relative to the control locus SHGC-79576 on 6p12, using fluorescence in situ hybridization (FISH). Deletion of 6q is observed in all types of B-cell malignancies, where two commonly deleted regions map to the A20 and PRDM1 gene region.^[1,2] Loss of the A20 gene has been observed in ~20% of non-Hodgkin lymphoma (NHL) cases, ~20% of mucosa-associated lymphoid tissue (MALT) lymphoma cases^[3] and in nonsplenic marginal zone lymphomas (MZLs) cases.^[4] The loss of the A20 gene has been observed most frequently in mantle cell lymphoma (MCL) and diffuse large B-cell lymphoma (DLBCL) cases with a frequency rate of 31% and 38%, respectively.^[5] In DLBCL, inactivation of is seen more frequently in the acti­vated B-cell (ABC) subtype of  (50%) versus the germinal center B-cell (GCB) subtype (22%).^[3,5,6] DLBCL cases exhibit a variety of complex 6q deletions, which encompasse either A20 or PRDM1 alone or together as part of a larger deletion.^[2] Additionally, the deletion of the PRDM1 gene has been observed in 53% of primary central nervous system lymphomas (PCNSLs).^[7,8]