Is Lupus genetic or is it like cancer? I don't really understand how does one get lupus?

Answer 1

Lupus is partly genetic but the environment plays a role as well.
No one is really sure what triggers lupus, but that link has theories. Scientists have proposed certain medications, smoking, too much stress, viruses, or even too much sun.
But none of these has been proven.

Answer 2

There appears to be some type of genetic predisposition to the development of systemic lupus erythematosus. It can appear more than once in the same family, but the data on its development is still not terribly clear. It can express a wide range of symptoms and effects from mild to severe. It would not be analogous to cancer. In its most basic terms, people suffering from Lupus have a problem with their immune system generating antibodies against their own cells and tissues.

Check this excelent link for more information:
www.medicinenet.com/systemic_lupus/article.htm