The nature of neural invasion by pancreatic cancer

Objectives: Neural invasion is one of the most important modes of tumor extension in pancreatobiliary tract cancer. However, the precise pattern of neural invasion and the relationship between neural invasion and nodal involvement are unknown. Methods: Using 8 surgical specimens from patients with pancreatic cancer, 4973 sections were created and examined histopathologically. A total of 961 sections of VX2 tumor grown in the retroperitoneum of rabbits also were examined histologically. The precise mechanism by which neural invasion occurs and the relationship between nerve fascicle and lymph node involvement were determined by histological examination of serial sections. Results: Histological evaluation of the surgical specimens revealed continuity between the cancer cells between the inside and the outside of the perineurium. Tumor cells grew mainly in a continuous fashion along the branches of nerves. An advancing tip of the tumor cells was identified. The pattern of tumor spread in the experimental study was similar to that in the clinical study. Continuity was found between the cancer cells inside some lymph nodes and the cancer cells within the perineural space. This finding suggests that neural invasion might be a pathway to lymphatic involvement. Conclusions: Neural invasion is a common, but not a specific, feature of pancreatic cancer. Tumor cells in the perineural space grow in a continuous fashion and may be responsible for some cases of lymphatic spread.