SNPS

SNP stands for "single nucleotide polymorphism". A nculeotide is one of the bases that makes up the genetic code. A polymorphism is a variation that is not very rare -- i think the general level is that they talk about "mutations" if it occurs in fewer than 1% of  the population; a "polymorphism" is a difference in the DNA sequence that occurs more often than 1%. Many SNPs are found in 10% or even 20% of people tested; most of them have no known effect -- because who's been looking? It's only in the past 10 yrs, since the human genome project got done, that we can look at these things.

So a SNP would be if, for example, in a nucleotide sequence that normally reads "....ACTGACTG..." one of the bases is different -- let's say "....ACTGA >>G<< TG...". And this same variation occurs in more than 1% of the population.

What scientists are finding is that some of these SNPs do make a difference in how the gene functions. It's a big thing in neuroscience -- they have SNPs that seem to be associated with impulsiveness, for instance, and the SNP does occur in a gene that codes for a neurotransmitter. (In looking at individual SNPs, t's not too much good looking at random; there are too many genes in the genome, and a lot of them seem to be inactive anyway. So it's really best to look at genes that have *some* connection to mechanisms.) But each SNP may have a very small effect, so now they're beginning to look at haplotypes -- combinations of SNPs that may add up to a pretty big effect.

I hadn't realized they are looking at SNPs for breast cancer -- as i said, it's a big thing in behavioral research, where they've really had no luck finding big-effect genes.  But it would make sense for breast cancer, too -- there are so many of us with a strong family history but not BRCA.... i've always assumed there were a bunch of small-effect genes running in my family. It would be really interesting to get into a project like that ...

I've never been tested, I don't even know how I'd go about doing it.

I found this interesting bit of info, to me at least since I take Femara (Letrozole). 

Scientists are also trying to determine how the presence or absence of SNPs affects response to drug treatments in a research subfield called pharmacogenomics. 

In 2008, researchers published data that found patients with breast cancer who were treated with letrozole had much better outcomes if they had the SNP rs4646. Specifically, the time to progression among the patients with this SNP was 17.2 months compared with 6.4 months in the patients without the SNP. 

http://www.aacr.org/home/public--media/patients--family/fact-sheets/cancer-concepts/snps.