For cancer patients, the risk of developing metastasis in vital organs brings a great deal of anxiety and uncertainty. After tumor cells are released into systemic blood circulation, metastasis can potentially develop in any organ that becomes the recipient of tumor emboli. However, extensive analysis of autopsy records in cancer patients revealed that the relative distribution of metastases in different organs is far from random. Certain organs, such as bone, lung, and liver, are frequently victimized by metastatic cancers, whereas other organs and tissues, such as the spleen and muscles, are rarely affected [1].

Metastasis organotropism is a term to reflect the well-documented fact that each type of cancer manifests a distinct pattern of metastatic involvement in secondary organs (Figure 20.1) [1, 2]. For example, almost 85 percent of advanced-stage prostate cancer patients suffer from bone metastasis. In contrast, liver metastasis is predominant among late-stage colorectal cancer patients, who rarely develop bone metastasis (Figure 20.1). Breast cancer often metastasizes to the bone, liver, and lungs; metastases to each of these organs were found in at least 25 percent of advanced-stage patients at the time of diagnosis (Figure 20.1) and in more than 60 percent at the time of autopsy [3]. Metastasis from the primary breast tumor to other distant organs, such as the kidney, spleen, or uterus, is relatively rare.