When iMMECs are stably transfected with wild-type Pak4, the resulting acinar structures exhibit increased cell proliferation and survival, filling of the luminal space with cells, increased acinar size, loss of cell polarity and a larger outer layer of epithelial cells.5 These changes are all hallmarks of precancerous conditions and early tumor stages, such as atypical hyperplasias and ductal carcinoma in situ (DCIS). This evidence concerns the gene PAK4 and ductal breast carcinoma in situ.