In ,
says...
Early detection and treatment of breast cancer is important.
That's a shame about your sisters. I'm sorry for them. It sounds like it could
have been hereditary. There is a test for the gene called the BRAC1 and/or BRAC2
which identify those with a higher probability of developing breast cancer:

"In 1994, the first gene associated with breast cancer - BRCA1 (for BReast
CAncer1) was identified on chromosome 17. A year later, a second gene associated
with breast cancer - BRCA2 - was discovered on chromosome 13. When individuals
carry a mutated form of either BRCA1 or BRCA2, they have an increased risk of
developing breast or ovarian cancer at some point in their lives. Children of
parents with a BRCA1 or BRCA2 mutation have a 50 percent chance of inheriting
the gene mutation."

http://www.genome.gov/page.cfm?pageID=10000507

My younger daughter wants to be tested, but there are then problems with
insurance if the tests prove positive.

Like being turned down for insurance for pre-existing conditions? Too
bad we don't have a national health insurance plan with open coverage
for everyone. You know, like people in most civilized countries have.