herceptin, is it the right choice?

My mother, age 56, underwent a radical mastectomy 1/01 with 9/18 axillary lymph nodes positive.  Follow-up testing showed the cancer was Her-2 + but est. and progest. neg.  Her oncologist is now claiming initial testing may have been inaccurate and cancer may not be reactive to herceptin.  She has undergone adriamycin, cytoxin, taxol, herceptin (weekly x 1 year) and 35 radiation treatments.  What would the error possibly be, and why would she need new testing for the HER-2 receptors/expression?  Were the test methods faulty in January?  She is wondering if she should quit the entire clinical trial. This worries me terribly, as everything I've learned about stage II HER-2 cancers suggests that this is a very aggressive cancer if there is recurrence.

[CCF-RN,MSN-rf]

Dear cbone:  There are different tests with varying sensitivity to measure Her-2 neu status.  I don't know why the change in opinion at this juncture.  It may make sense to have the tumor retested for her/your own peace of mind.  If it is positive, you will feel more confident.  If it is negative, you may want to discuss with an oncologist whether she should continue with the herceptin.  It looks as though she has completed the rest of the treatment already.  You are right, Her-2 neu positive cancers tend to be aggressive.  If you confirm positivity - she is probably fortunate to have been randomized to this arm of the study.