Breast Biomarker Cytology Practice in 2023: Results of a College of American Pathologists Survey.

Context.—: The College of American Pathologists (CAP) surveys provide national benchmarks of pathology practice.

Objective.—: To investigate breast biomarker cytology practice in domestic and international laboratories in 2023.

Design.—: We analyzed data from the CAP Breast Biomarker Cytology Practice Supplemental Questionnaire that was distributed to laboratories participating in the 2023 CAP Nongynecologic Cytopathology Education Program.

Results.—: Twenty-five percent (180 of 728) of responding laboratories routinely evaluated breast biomarkers in cytology specimens. Breast biomarkers evaluated in cytology specimens included estrogen receptor/progesterone receptor (98.9%; 175 of 177), human epidermal growth factor receptor 2 (HER2) (93.2%; 165 of 177), Ki-67 (48.6%; 86 of 177), programmed death ligand-1 (PD-L1) (20.9%; 37 of 177), and mismatch repair (19.8%; 35 of 177). Fine-needle aspiration was the most validated specimen type (85.3%; 133 of 156), followed by body fluids (82.1%; 128 of 156). All respondents validated cell blocks (100.0%; 165 of 165), with a few laboratories also validating cytospin slides (3.0%; 5 of 165), liquid-based slides (3.0%; 5 of 165), air-dried direct smears (2.4%; 4 of 165), and others. CytoLyt was the most used collection medium (55.4%; 87 of 157), followed by balanced salt solution (16.6%; 26 of 157), Roswell Park Memorial Institute Medium (13.4%; 21 of 157), and CytoRich Red (9.6%; 15 of 157). Almost all laboratories indicated routinely using formalin (90.4%; 151 of 167) as fixative, while a few laboratories used other types of fixative (ethanol [5.4%; 9 of 167], methanol [3.0%; 5 of 167]). Digital imaging platforms were used by only 12.9% (22 of 171) of responding laboratories. Forty-four laboratories (28.0%; 44 of 157) required cellularity adequacy for interpreting breast biomarkers on cytologic specimens. Additionally, some significant differences in breast biomarker testing practice were identified among different institution types and between domestic and international laboratories.

Conclusions.—: This is the first survey from the CAP to investigate breast biomarker cytology practices. The findings reveal some differences among institution types and between domestic and international laboratories. These data provide a baseline for and support further studies and/or guidelines to promote and refine these practices.