Increased surgical stress promotes tumor metastasis

Although it is well-known that excessive surgical stress augments the growth of residual cancer and metastasis, whether surgical stress is increased according to the degree of surgical manipulation and can consequently lead to the enhancement of cancer metastasis has not been thoroughly examined. Moreover, the molecules associated with response for stress-enhanced metastasis have not been well-analyzed. The aim of this study was to examine whether cancer metastasis is enhanced with an increase of surgical stress with an experimental lung metastasis model and to analyze the related molecules responsible for stress-enhanced metastasis.

Colon 26-L5 carcinoma cells (1.5 x 10(4)/mouse) were injected intravenously into 6-week-old female BALB/c mice (Japan SLC, Hamamatsu, Japan). Two hours later, the mice were divided into 5 groups: untreated controls (the C group); mice given anesthesia only (the A group); mice given anesthesia and laparotomy (the AL group); mice given anesthesia, laparotomy, and appendectomy (the ALAp group); and mice given anesthesia, laparotomy, appendectomy, and left hepatic lobectomy (the ALApH group). The anesthesia procedures were the same in all groups (intraperitoneal administration of 0.8 mg/mouse sodium pentobarbital). In the AL, ALAp, and ALApH groups, a 3-cm long laparotomy was performed, and the time of the whole operation was just 5 minutes. All mice were killed 14 days after the procedures, and the number of lung metastases on the lung surface was counted manually. At the same time, BALB/c mice without tumor burden were given the same 5 kinds of surgical stress, and the messenger RNA expression of various metastasis-related molecules in the lung was measured with reverse transcriptase-polymerase chain reaction at 6, 24, and 48 hours after surgical stress. We also examined the effect of ONO-4817 (an inhibitor of matrix metalloproteinases ([MPs]) on lung metastasis in the mice with the 5 kinds of surgical stress.

The numbers of lung metastases on the lung surface and the messenger RNA expression of MMP-9, membrane type IBMMP, and urokinase-type plasminogen activator at 24 hours after surgery were enhanced in proportion to the degree of surgical stress. Moreover, ONO-4817 significantly inhibited lung metastasis.

These results strongly suggest that increased surgical stress augments cancer metastasis via surgical stress-induced expression of proteinases in the target organ of metastasis.