Comparison of 8G7G3/1 and SP141 TTF-1 MAbs
| Tissue | 8G7G3/1 MAb: n (%) | SP141 MAb: n (%) |
|---|---|---|
| Normal lung—alveolar epithelium | 7/7 | 7/7 |
| Adenocarcinoma of the lung | 35/35 | 35/35 |
| Atypical squamous lesions—12 SCCs+1 case of bronchial squamous dysplasia | 0/13 | 5+1/12+1 (∼46%) |
| Pleomorphic/sarcomatoid carcinoma of the lung (spindle-cell component only) | 2/12 (17%) | 4/12 (∼33%) |
| Epithelioid malignant mesothelioma | 0/66 | 0/66 |
| Sarcomatoid mesothelioma | 0/19 | 8/19 (∼42%) |
We are unaware of any systematic data on the actual levels of TTF-1 expression in, for example, sarcomatoid carcinomas of the lung and sarcomatoid mesotheliomas, for estimation of the rates of true/false positive/negative IHC labelling of these tumours. Existing evidence indicates that positive IHC labelling for TTF-1 protein may not represent ‘false’-positive labelling, but rather ‘true’ labelling in these cancers (ie, detectable labelling represents high affinity of the SP141 MAb in particular for low levels of TTF-1 protein in different cancers, with loss of diagnostic specificity for tumour classification by IHC). Ideally, these assessments should be made in comparison with true zero/augmented levels of mRNA as the template for TTF-1 protein—and as such the ‘gold standard’ test—but to the best of our knowledge, systematic data on mRNA levels in these sarcomatoid tumours are unavailable (see text).
IHC, immunohistochemical; MAb, monoclonal antibody; SCC, squamous cell carcinoma; TTF-1, thyroid transcription factor-1.