In patients with invasive breast carcinoma, estrogen receptor α (ERα) and progesterone receptor (PR) expressions need to be assessed in core-needle biopsies (CNBs) before the start of neoadjuvant systemic treatment. Current guidelines recommend a minimum formalin fixation time of 6 hours. Considering the increasing demand for same-day diagnostics in oncology, more rapid tissue processing with shorter fixation times is required. To identify whether brief fixation (<6 h) of CNBs compared with conventionally fixed resection specimens provides for reliable immunohistochemical assessment of ERα and PR expression, 78 consecutive patients diagnosed with invasive breast carcinoma were included through the same-day diagnostics programme of the UMC Utrecht. Paraffin-embedded CNBs fixed for approximately 45 minutes were retrieved. Immunohistochemistry for ERα and PR was compared between the briefly fixed CNBs and conventionally fixed resection specimens. All slides were reviewed by means of consensus scoring by 2 blinded observers. Overall agreement between CNB and resections was 73/74 (98.6%) for ERα (κ=0.85; 95% confidence interval [CI]=0.56-1.00) and 69/75 (92.0%) for PR (κ=0.81; 95% CI=0.66-0.96). For ERα, positive and negative predictive values were 98.6% (95% CI=0.91-0.99) and 100.0% (95% CI=0.31-1.00), respectively. For PR, positive and negative predictive values were 100.0% (95% CI=0.91-1.00) and 76.0% (95% CI=0.54-0.90). In conclusion, analysis of hormone receptor expression in briefly fixed CNB seems comparable to results from conventionally fixed resection specimens of the same tumor.