Fig. 2
From: Factors involved in cancer metastasis: a better understanding to “seed and soil” hypothesis
Soil factors, both primary soil factors and secondary soil factors are depicted here. Primary soil factors promote metastasis by enhancing the metastatic potential of seed. A variety of stromal cells and other molecular components surrounding the primary tumor provide signals to enhance the invasion properties of cancer cell. In addition, hypoxia in primary soil also play a crucial role in accelerating cancer metastasis. The secondary soil is composed of many factors and cell types in specific soil. The fertile cellular and molecular components in lung, liver, bone, brain, which play a pivotal role in inducing seed, invasion, eventual colonization and outgrowth at distant sites are depicted here