Updated Colorado score for scoring and interpreting clusters (adapted from Varella-Garcia, 200628)
| Pattern description | Scoring criteria | Expected ratio EGFR to CEP7 in the specimen | EGFR FISH classification* |
| Large clusters of EGFR signals | Count signals thoroughly and calculate the indexes. If number of signals is >15, write “16” | >2 | Classify as positive (GA) if EGFR/CEP7 ratio ⩾2 or if clusters of EGFR signals are present in ⩾10% cells |
| Small clusters of EGFR signals (⩾4 signals) | Count signals thoroughly and calculate the indexes | >2 to ∼1 if high level of aneusomy 7 is present | Classify as positive (GA) if EGFR/CEP7 ratio ⩾2 or if clusters of EGFR signals are present in ⩾10% cells |
| Co-localised clusters of EGFR and CEP7 signals | Count signals thoroughly and calculate the indexes. If number of signals is >15, write “16” | ∼1 | Classify as positive (GA) if clusters are present in ⩾10% cells |
| Very high number of balanced red (EGFR) and green (CEP7) signals | Count signals thoroughly and calculate the indexes | ∼1 | Classify as positive (GA) if ⩾10% cells have ⩾15 EGFR signals |
| EGFR as double minutes | Count signals thoroughly and calculate the FISH indexes | >2 | Classify as positive (GA) if EGFR/CEP7 ratio ⩾2 or ⩾10% cells have ⩾15 EGFR signals |
EGFR, epidermal growth factor receptor; FISH, fluorescence in situ hybridisation; GA, EGFR gene amplification.