Determination of transforming growth factor beta1 mRNA expression in breast carcinomas by in situ hybridization

The expression of transforming growth factor beta1 (TGF‐β1) mRNA has been determined in 16 breast carcinomas using in situ hybridization and compared with TGF‐β protein as detected by antibodies against TGF‐βT1 and TGF‐β1 plus TGF‐β2. Digoxigenin‐labelled riboprobes were used, with alkaline phosphatase and immunogold silver detection systems. TGF‐β1 mRNA was only detected in carcinomas in which TGF‐β1 protein was found (9 of 16 cases) and not in those with prominent reactivity for TGF‐β2. RNA preservation was poor in two other cases in which TGF‐β1 protein had been detected. In general, those tumours with greater numbers of cells labelled for TGF‐β1 mRNA had prominent reactivity for TGF‐β1 protein. The mRNA was localized to cancer cells with no labelling of stromal cells, although in a small number of cases scanty staining for TGF‐β1 protein had been observed in stromal cells. The incidence of detection of TGF‐β1 mRNA is lower than the published data from Northern analysis studies of breast carcinomas, suggesting that only higher levels of TGF‐β1 mRNA expression are being detected by in situ hybridization. However, this approach has provided useful information about the cellular sites of expression of TGF‐β1 in breast carcinomas.