ER/PR/Her2 are often reflexively assessed in all core needle biopsies (CNBXs) containing invasive mammary carcinoma (IMC) so that neoadjuvant therapy can be considered. ER/PR/Her2 can be heterogenous, and there is growing consensus that negative results for any of these markers in small CNBXs should be repeated in larger excision specimens (EXS). The frequency and added cost of repeat testing of EXS containing untreated IMC with negative ER/PR/Her2 CNBX results has not previously been studied. We reviewed 198 CNBXs containing IMC, which had reflex ER/PR/Her2 testing and for which there was an EXS for review. We determined the number of cases in which ER/PR/Her2 immunohistochemistry and Her2 fluorescence in situ hybridization were negative on CNBX. Twenty-seven (13.6%) patients received neoadjuvant chemotherapy, and 8 (4%) patients did not have IMC on follow-up EXS, so for them testing the CNBX was necessary. Of the remaining 163 IMCs, 17% were ER negative, and 26% were PR negative, whereas 85% were Her2 negative or equivocal. At our institution, ER/PR were repeated on slightly more than one half of ER/PR-negative tumors, whereas Her2 was repeated on less than one third of Her2-negative/equivocal tumors. Had all negative tests been repeated, the increased cost of testing both the CNBX and EXS would be $100,821. Extrapolating to 230,000 new cases of IMC in the United States each year, the increased cost of repeat testing of all negative ER/PR/Her2 CNBX results would be >$117 million dollars. Limiting reflex testing to ER would decrease the cost of repeat testing to $10 million dollars. We suggest that ER/PR/Her2 should not be reflexively performed on all CNBX specimens containing IMC but instead be routinely performed on EXS and only selectively on CNBX specimens if neoadjuvant chemotherapy is a serious consideration for that individual patient.