While the presence and degree of arm edema can, in part, correlated with the extent of axillary surgery, we still comprehend only poorly the factors that predispose to overt lymphatic insufficiency in the patients at risk for lymphedema by virtue of prior breast cancer treatment. It is likely that this anatomic and regenerative variability relies, at least in part, upon an as yet undefined genetic substrate. A growing body of evidence suggests that mutations in the nuclear transcription gene FOXC2 are responsible for a broad clinical array of primary lymphedema syndromes. The biology of breast cancer-associated lymphedema, including its characteristic latency phase, suggests that similar mechanisms may operate in the predisposition to this and other forms of secondary lymphedema.