Suggested algorithm for pulmonary non-small cell carcinoma without clear morphology when TTF-1 clone SPT24 is used
| p40 | |||
| TTF-1 clone SPT24 | <10% | 10%–49% | ≥50% |
| <10% | Undetermined, add broad CK and so on | Probably SqCC, add CK5 and napsin A | SqCC |
| 10%–49% | AC | Undetermined, add CK5 and napsin A | Probably SqCC, add napsin A |
| ≥50% | AC | Probably AC, add CK5 and napsin A | Probably SqCC, add napsin A |
Consider NE tumour if p40 <50%; no pattern rules out metastasis to the lungs.
AC, adenocarcinoma; CK, cytokeratin; SqCC, squamous cell carcinoma; TTF-1, thyroid transcription factor-1.