Cancer that spreads outside the prostate gland is what makes prostate cancer dangerous. Metastatic prostate cancer cells cause malfunction by impeding normal function. Some organs, like lymph nodes for example, continue to function quite nicely, even if the degree of cancer spread is extensive.  Lymph node spread, therefore, is the least dangerous form of prostate cancer metastases.  At the other end of the spectrum is the liver, which is far less tolerant.  The seriousness of bone metastases, the most common site of prostate cancer spread, lies about half way between that of node metastases and liver metastases.