Molecular mechanisms of perineural invasion, a forgotten pathway of dissemination and metastasis.

Invasion and metastasis are key components of cancer progression. Inflammatory mediators, including cytokines and chemokines, can facilitate tumor dissemination. A distinct and largely forgotten path is perineural invasion (PNI), defined as the presence of cancer cells in the perinerium space. PNI is frequently used by many human carcinomas, in particular by pancreas and prostate cancer, and is associated with tumor recurrence and pain in advanced patients. Neurotrophic factors have been identified as molecular determinants of PNI. A role for chemokines in this process has been proposed; the chemokine CX3CL1/Fractalkine attracts receptor positive pancreatic tumor cells to disseminate along peripheral nerves. Better understanding of the neurotropism of malignant cells and of the clinical significance of PNI would help the design of innovative strategies for the control of tumor dissemination and pain in cancer patients.