Determining causality requires measuring the virus infection in the context of these factors rather than infection alone. ...EBV infection alone does not cause cancer but EBV infection of a post-germinal B cell having a c-Myc rearrangement does. An analogous pathway is shown for the genesis of Burkitt lymphoma, in which EBV is responsible for a portion of tumors, but also only in the biological context of other factors, such as cMYC translocations. Since EBV is nearly ubiquitous, teasing out its contribution to a rare cancer like Burkitt lymphoma is supremely difficult using standard epidemiologic methods, but is readily evident using molecular biologic information that has been available for decades.