Colorectal cancer: seed and soil hypothesis revisited.

The local growth and metastatic potential of colorectal cancer is the outcome of a dynamic balance between cancer cells and the immune system, at both a local and systemic level, summarized as the "seed and soil" hypothesis. Until recently, the staging and treatment approaches for colorectal cancer appeared to be orientated predominantly to the 'seed' component, virtually neglecting, in daily clinical practice, the impact of the 'soil' in the natural course of the disease. We are currently witnessing an increasing amount of evidence, spanning from clinical to laboratory research, which highlight that cancer growth and metastasis is the result of the dynamic balance between the disease itself and the impaired function of the immune system. Herein, we attempt to elucidate the vicious circle between impaired immune response and colorectal cancer progression, highlighting the urgent need for a qualitive turn in confronting cancer, which is based on two pillars with regulation of both the seed and the soil.