Salk Institute -- Wahl Lab -- Cell Atlas (IMAGE) Salk Institute Caption Pictured is mammary tissue of a developing mouse embryo at day 18, with cells that express both luminal protein (red) and basal protein (green). Cells in breast cancer often show this embryonic characteristic of expressing both proteins. Credit Salk Institute Usage Restrictions with credit and related coverage. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.