Friends or foes - bipolar effects of the tumour stroma in cancer.

The restricted view of tumour progression as a multistep process defined by the accumulation of mutations in cancer cells has largely ignored the substantial contribution of the tumour microenvironment to malignancy. Even though the seed and soil hypothesis of Paget dates to 1889, it has been less than two decades since researchers have included the tumour microenvironment in their analyses of tumour progression. What have we recently learned from studying tumour-stroma interactions, and will this help to define new targets for therapy?