Immunohistochemical pattern of c-MYC protein judged as “+/(weak)+/−” by a new notation correlates with MYC gene nontranslocation in large B-cell lymphoma

Summary Immunohistochemistry is not only the most important tool for pathologists to establish a final diagnosis, but it can also inform decisions regarding optimal treatment methods. However, there is no universal standard notation for expressing immunohistochemical findings. For a diagnosis of malignant lymphoma, it is important to confirm the presence or absence of MYC translocation and communicate these results to a clinical audience. However, the criteria for selecting cases for fluorescence in situ hybridization (FISH) analysis to confirm MYC translocation are ill defined. We therefore devised a notation that we termed proportion of immunoreactivity/expression for immunohistochemistry (PRIME notation) based on the cellular proportion showing different antigen-antibody reactivity in immunohistochemistry (CPAR) and used it to examine the relationship between MYC translocation and the proportion of c-MYC+ lymphoma cells. We reviewed 82 cases diagnosed as diffuse large B-cell lymphoma or diffuse large B-cell lymphoma coexisting with grade 3A to 3B follicular lymphoma. The most common notation was “+/(weak)+/−” (49/82 cases [59.8%]); cases that were CPAR positive, weakly positive, and negative for tumor cells each accounted for about one-third of the total. Unexpectedly, no MYC translocation was observed by FISH in this group. Thus, FISH is not needed even if more than half of cells are c-MYC positive by PRIME notation. This is the first report describing a correspondence between immunohistochemical findings and chromosomal abnormality, reflecting findings at the protein and gene levels, respectively.