Interpretive disparity among pathologists in breast sentinel lymph node evaluation

Immunohistochemical staining on breast sentinel lymph nodes (SLN) is controversial. Twenty-five SLN cases were reviewed by 10 pathologists (three academic, seven private) including 5 negative by both hematoxylin and eosin (H&E) and immunohistochemistry, 11 micrometastases (2 mm) positive for both H&E and immunohistochemistry. Answers included "positive," "negative," and "indeterminate" for each slide. The mean number of incorrect responses was 6.6 for immunohistochemistry and 5 for H&E. Twelve percent of cases were correct by all 10 pathologists; 80% of positive IHC cases had at least one pathologist score it incorrectly. As tumor cells decrease in number, incorrect responses increase. When tumor cells numbered less than 10, more than 30% of pathologists answered incorrectly. As tumor cells decrease in number pathologists' ability to recognize them decreases. We propose adding "indeterminate" to "positive" and "negative" when tumor cells number less than 10.