Diagnostic accuracy in surgical pathology is fundamental to patient care. Defining and classifying diagnostic errors is challenging because of the absence of universally accepted definitions and variability in their causes and outcomes. An error is considered to occur when the pathology service falls below the expected standard of care. This standard is not fixed and depends on factors like clinical context, case complexity, and available diagnostic resources. Most definitions of diagnostic error focus on whether there has been a clinically meaningful change in diagnosis, treatment, or patient outcome. Despite these challenges, true diagnostic errors, specifically those with significant clinical consequences, are relatively uncommon.
Evidence from large studies shows that major diagnostic error rates in surgical pathology typically range from 1.5 to 5.7%. Real- case reviews report lower rates between 0.26 and 1.2%, which highlight the value of ongoing quality checks before final diagnosis. Retrospective studies, specifically those that involved blinded re-evaluation of previously reported cases, tend to show higher error rates of about 4%, although these differ by sample type and diagnostic difficulty. Clinically significant errors, those that directly affect patient management, are rare, generally occurring in >1% of cases. Higher rates may be observed in studies focusing on complex or borderline lesions, where interpretation is inherently more difficult.
Breast pathology shows this complexity well. In routine practice, discrepancies between initial and review diagnoses that affect patient management are typically >3%. In referral or second-opinion settings, where more challenging cases are concentrated, discrepancy rates can exceed 10%. These higher rates do not necessarily reflect poor diagnostic performance but instead the complexity and ambiguity of specific lesions. Therefore, it is essential to interpret diagnostic error rates in context, as raw figures alone can be misleading and may contribute to misunderstanding.
A key aspect of pathology practice is distinguishing true errors from acceptable interobserver variability. Not all differences in diagnosis represent mistakes; many fall in a reasonable range of professional interpretation, specifically in cases with overlapping or ambiguous features. Discrepancies that lead to major diagnostic changes or altered treatment decisions can have significant clinical and medicolegal implications. For this reason, evaluating concordance should consider both the degree of disagreement and its impact on patient care.
Technological advancements are helping to reduce diagnostic errors and improve workflow efficiency. Automation, digital pathology, and artificial intelligence (AI) tools enhance multiple stages of the diagnostic process. Automated sample tracking and barcoding reduce preanalytical errors like mislabelling. Digital slide systems improve accessibility and efficiency. AI-assisted tools can support the detection of subtle abnormalities and help prioritize urgent cases. Although these technologies do not replace expert judgment, they act as valuable aids to improve consistency and reduce variability.
Quality assurance methods also play an important role in reducing errors. Root cause analysis helps to detect factors contributing to discrepancies, including case complexity, sampling limitations, workflow inefficiencies, and differences in expertise. Regular audits, participation in external quality assurance programs, and multidisciplinary discussions support continuous improvement and help to maintain high diagnostic standards.
It is important to distinguish between diagnostic errors, acceptable variability, and negligible form from a medicolegal perspective. Most errors are unintentional and occur from complex, multifactorial influences instead of misconduct. When an error leads to patient harm and reflects a violation of the standard of care, it may constitute negligence. Establishing this needs proof of both a breach of duty and a causal link to harm. Patient outcomes alone do not always reflect diagnostic quality, as even proper decisions may result in adverse effects.
Transparency is essential to maintaining trust. The Duty of Candour needs disclosure of significant errors that affect patient care, while non-harmful errors must still be reviewed to improve systems and processes. Although diagnostic errors in surgical pathology are relatively rare, they carry important implications. Strengthening quality systems, adopting new technologies, and fostering a culture of openness and continuous learning are key to improving diagnostic accuracy and patient safety.
Reference: Rakha EA, Quinn CM, Provenzano E, Pinder SE, Ellis IO. Diagnostic discordance and error in breast pathology: causes, classifications, and medicolegal implications. Mod Pathol. 2026;39(1):100942. doi:10.1016/j.modpat.2025.100942
