Detection of occult sentinel lymph node micrometastases by immunohistochemistry in breast cancer. An NSABP protocol B-32 quality assurance study.

BACKGROUND

Occult metastases, by definition, are not detected on initial examination. They may be present on slides but missed during screening or may be present in paraffin embedded tissue blocks and undetected without additional levels. Anticytokeratin immunohistochemistry (CK IHC) enhances detection of occult metastases, particularly micrometastases (> 0.2 mm but not larger than 2.0 mm) or isolated tumor cell clusters (< or = 0.2 mm). This study defines the rate at which pathologists miss metastases on CK IHC of sentinel lymph nodes (SLN).

METHODS

CK IHC sections 0.5 and 1.0 mm from the original surface of SLN tissue blocks were screened by pathologists using standard bright field light microscopes (LM) and by supervised computer assisted cell detection (CACD). All blocks were from breast cancer patients, initially classified 'node negative' on review of routinely stained sections from the surface of each block. Cases missed by LM screening but detected by CACD defined false negative screens.

RESULTS

Of 236 cases screened, LM detected 34 (14.4%; 95% CI: 9.6-20.2) cases and, in the 202 cases negative by LM, CACD detected an additional 30 (14.9%; 95% CI: 9.6-21.2%) cases with occult metastases. Occult metastases missed by LM screening ranged from 0.01 to 0.1 mm in greatest dimension. The probability of missing an occult metastasis < or = 0.02 mm; < or = 0.05 mm, and < or = 0.10 mm was 75%, 69.2%, and 61.2%, respectively. No occult metastases larger than 0.10 mm were missed by LM screening.

CONCLUSIONS

Pathologists screening the CK IHC stained slides may frequently miss detecting metastases < 0.10 mm.