[Assessment of proliferation: core biopsy or resection specimen? Discrepancies in breast cancer with low and high...

The assessment of the proliferation fraction is becoming more and more important; however, there is no consensus concerning optimal validation. Depending on the institute the proliferation fraction is determined either from a core biopsy (SB) or resection specimen (OP).

The interobserver variability and the results of SB and OP were investigated whereby two pathologists independently estimated the proliferation fraction of 90 cases of invasive breast cancer. The results (Ki-67) were quantified, categorized, and compared.

Identical (accuracy of 5% steps) results between the 2 pathologists were achieved in 43% (n=39) for SB, 47% (n=42) for OP and 60% (n=54) for SB versus OP. When categorizing the proliferation fraction (low  ≤ 15%, moderate 20-30% and high  ≥ 35%) the following results were achieved: 76% (n=68) for SB, 82% (n=74) for OP and 81% (n=73) for SB versus OP.

There was a clear interobserver variability (SB: kappa=0.32, OP: kappa=0.34) but this could be dramatically improved by forming proliferation categories (SB: kappa=0.62, OP: kappa=0.72, 60 versus 81%). In SB with a low proliferation fraction a repeated analysis in OPs can be advisable as a higher proliferation fraction is observed in up to 12% of OPs.