Tou Pin Chang, The Hamlyn Centre, Institute of Global Health Innovation, Imperial College London, London, UK.

•The aim of this study was to demonstrate the feasibility of pCLE imaging using freshly excised breast tissues, and clarify the ability of pathologists and surgeons to differentiate pCLE morphological images of neoplastic from non-neoplastic breast tissues using an in-house developed classification, towards intraoperative in situ margin assessment.

•Freshly excised tumour samples and adjacent non-diseased sections from 50 consenting patients were stained with 0.01 % acriflavine hydrochloride and imaged using pCLE.
•All discernible pCLE features were cross-examined with conventional histopathology. Following pattern recognition training, 17 histopathologists and surgeons with no pCLE experience interpreted 50 pCLE images independently whilst blinded to histopathology results. Three-hundred and fifty pCLE image mosaics were analysed.
•Consistent with histopathology findings, the glandular structures, adipocytes and collagen fibres of normal breast were readily visible on pCLE images. These were distinguishable from the morphological architecture exhibited by invasive and non-invasive carcinoma.

•The mean accuracy of pCLE image interpretation for histopathologists and surgeons was 94 and 92 %, respectively.
•Overall, inter-observer agreement for histopathologists was ‘almost perfect’, k = 0.82; and ‘substantial’ for surgeons, k = 0.74.

•pCLE morphological features of neoplastic and non-neoplastic breast tissues are readily visualized and distinguishable with high accuracy by both histopathologists and surgeons. Further research is required to investigate a potential role for the use of pCLE intraoperatively for in situ detection of residual cancerous foci, thereby guiding operating decision-making based on real-time breast cavity scanning.