Do you know what causes lymphoma?

Hard to say...: Most of the times we don't know what exactly causes lymphoma so there isn't much we can do to prevent it. Most cases probably have a genetic component but the process is probably multifactorial and many other things need to happen in order to produce lymphoma. In a small subset of cases, a distinct cause appears to exist: exposure to toxins, radiation, certain viruses (ex: ebv).

Like other cancers..: lymphoma arises from an unlucky combination of genetic mutations in lymphoid cells during our lifetime. Risk factors include exposure to toxins, family history, or a severe immune suppression (e.g. HIV). Most often, the proximal cause can not be determined, and is mostly just bad luck, since our body is naturally subjected to millions of genetic mutations over our lifetime.