Scientists have created a new strain of mice lacking cyclin D1, a vital component of the growth machinery in all cells, and found that knocking out this important cog causes surprisingly little damage. These results have implications for treating human breast cancer and should lead to a better understanding of the molecular basis of cancer. The study, reported in the August 25 issue of Cell, was carried out in the laboratory of Dr. Robert Weinberg, a cancer research pioneer at the Whitehead Institute for Biomedical Research.