Table 4.

Reasons for treatment with trastuzumab for 26 patients without a positive HER2 test result in the electronic tumor registry file

Tumor registry result	Chart review result
Missing HER2 test result (10 patients)	7 patients had recurrent breast cancer with a positive HER2 test result at recurrence, although not at initial diagnosis. 6 patients were diagnosed prior to 2000 before HER2 testing became systematically used at initial diagnosis. 2 patients received HER2 testing outside of KPNW. 1 patient showed no evidence of treatment with trastuzumab.
Negative HER2 test result (7 patients)	6 patients had a positive HER2 test result. 4 of these patients had multiple primary tumors, and the negative HER2 result corresponded to a different tumor than the one testing positive. 1 patient had an equivocal HER2 test result for both FISH and IHC, and the physician decided to treat with trastuzumab.
Equivocal HER2 test result (9 patients)	5 patients had a positive HER2 test result. In 3 patients physician notes documented a decision to treat with trastuzumab based on the equivocal HER2 result. 1 patient received all treatment outside the KPNW system.