[Lani]

If your serum her2 WERE drawn BEFORE the herceptin was started a repeat serum her2ECD AND approx 3 weeks later, and decreased 20-25%--it is regarded as a sign of herceptin efficacy in the metastatic setting (serum her2ECD is rarely elevated above 12 in the nonmetastatic setting as far as they know--there was just an article published in December confirming something similar in the neoadjuvant setting) according to a paper with Dr. Slamon among the authors.
If yours was drawn after starting herceptin and at no other time, repeating it counldn't hurt. If yours was drawn before starting herceptin, retesting it would probably make sense.

There are two new papers (one out today) on prognostic factors for herceptin efficacy--one based on genes and chromosomal evaluation claiming the length of the piece of DNA on which her2 sits which is amplified and whether there are simultaneous chromosomal abnormalities on chromosome 1 and 10 help predict the 40% of Her2(FISH+) amplified patients for whom herceptin produced a beneficial effect in the metastatic setting. The second paper (out today) evaluated the relationship between positivity of other her family members, phosphorylation of her2 (p-her2, the activated form), and other biomarkers is based on testing by IHC(much easier to find available, although still done by only a few labs) and
clinical benefit from herceptin ie, once again how to predict which 40% will benefit from Herceptin. Interestingly the second article was coauthored by Martine Piccart of Belgium (head of the HERA study) and someone from Roche (who sell herceptin in Europe). Should they be able to predict herceptin sensitivity, they may lose some herceptin sales, but European governments may be more welling to pay for it for fewer people(those who it is more likely to help) and hopefully will look into using something else
(?lapatinib) for the others.

Hope this helps!