Table 5.
Discordant STRAT4-ESR1 vs IHC-ER Cases and STRAT4-ERBB2 vs IHC-HER2 Cases by Tumor Area and Cellularitya
| Tumor Area, No. | Tumor Cellularity, No. | ||||
|---|---|---|---|---|---|
| Characteristic | Very Small (≤25 mm2) | Small (26-≤50 mm2) | Large (≥51 mm2) | Low (≤50%) | Normal (≥51%) |
| Cases | 51 | 43 | 56 | 32 | 118 |
| ER-IHC STRAT4-ESR1 1× discordant | 6 (of 12) | 3 | 2 | 4 | 8 |
| ER-IHC STRAT4-ESR1 4× discordant | 6 (of 12) | 3 | 1 | 4 | 8 |
| Discordant HER2-IHC STRAT4-ERBB2 | 2 (of 3) | 0 | 1 | 1 | 2 |
aApproximately one-third of tumors fell in each tumor area category, but discrepant cases were disproportionately in the very small tumor area samples. Low tumor cellularity defined as 50% or less of tumor area occupied by tumor cells was not a notable issue in discrepant cases.