I'm not sure which study you refer to. I would love to have a look at it. There are a huge number of confounding factors which may, or may not have been taken into account here. For example, breast cancer risk is also increased if the individual has never had children/breast fed. Is the rate different in flight attendants because of this? Or is it an age effect (also related to the risk as slim_slag said). You can "prove" anything you want with statistics. It is how carefully the analysis is carried out that maters.
Cheers,
BM