How does the nervous system influence the tumor metastasis?

In a very interesting paper by Li et al (2013) the connection between tumor metastasis and the nervous system was summarized. The illustrated connection is vital and operates through different mechanism to influence the spread of tumor cells.

The paper starts by describing what was previously thought as non-existent process: the neuro-neoplastic synapses; nerve cells growing in the tumor as a part of the tumor itself. These neoplastic nerve cells are unlike the pre-existing nerves which do not affect tumor metastasis and result in the pain experienced by cancer patients if invaded by the malignant cells. This direct influence exerted by the nervous system is combined with other indirect influences such as affecting angiogenesis and tumor micro-environments, interaction with immune function and inflammation factors, and interaction with bone marrow to facilitate tumor growth and spread.

A very informative article to read: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3629128/