Interpretive disparity among pathologists in breastsentinel lymph node evaluation

Background Immunohistochemical staining on breast sentinel lymph nodes (SLN) is controversial. Methods 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) negative by H&E but positive by immunohistochemistry, and 8 micrometastases and 1 macrometastasis (>2 mm) positive for both H&E and immunohistochemistry. Answers included “positive,” “negative,” and “indeterminate” for each slide. Results 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. Conclusions As tumor cells decrease in number pathologistsʹ ability to recognize them decreases. We propose adding “indeterminate” to “positive” and “negative” when tumor cells number less than 10.