Interobserver Variability in the Measurement of the Metastatic Tumor Size on Breast Sentinel Lymph Nodes.

Context.—: Accurate measurement of breast cancer metastatic deposits in sentinel lymph nodes (SLNs) can be challenging despite the presence of guidelines.

Objective.—: To assess interobserver variability in measuring metastatic breast carcinoma involving axillary SLNs.

Design.—: A survey of 10 microscopic images of lymph nodes involved by metastatic carcinoma was electronically shared with a large group of practicing pathologists. Images were all taken at ×1 or ×10 magnification from AE1/3-stained slides. Three options were included on how to measure metastatic foci (a, b, c) without providing the size. A fourth option for uncertain responses was included (not sure/other, d).

Results.—: A total of 88 pathologists completed the survey. We observed significant variability regarding how metastatic deposits are measured. Cases with extracapsular extension were prone to more variability (cases 5, 9, 10) with a significant number of the responders demonstrating uncertainty or excluding the extracapsular extension from the metastatic size.

Conclusions.—: Our results underscore the inherent difficulty and thus the interobserver variability that exist when measuring and classifying small metastatic tumor deposits in SLNs, even when definitive guidelines have already been established.