How can a religion be an ethnicity... with all respect?! Please no rude or mean comments!?

If I am correct (I am not really well versed in this area), there are some Jewish people (possibly the Ashkenazi that you mentioned) who believe you can only be Jewish if your Mother was/is Jewish. This then means that the Jewish line is created via a blood link. It's not exactly the same as ethnicity, but would explain why there can also be a link to a higher risk of cancer for these people - as they would share some of their gene pool.