French researchers have found an association between how well the body responds to colon tumors and survival among more than 400 patients with the disease. They suggest that analyzing tumors for the presence of certain immune cells could yield valuable prognostic information for patients.

The results support the theory that the immune system may influence the behavior of tumors. In recent years, studies of ovarian cancer and follicular lymphoma have suggested that the presence or absence of certain immune cells in tumors can be used to predict the survival of patients with these diseases.

The new study expands this research to colorectal cancer. Like the others, it focuses on the presence of T cells in tumors; these immune cells react to specific threats to the body.

"Our data reveal that the immune reaction at the tumor site determines the cancer's evolution and clinical outcome regardless of the local extent and spread of the tumor," says co-lead investigator Dr. Jerome Galon of the French National Institute of Health and Medical Research, or INSERM.

The study included 415 colorectal tumors from patients with known medical histories. The researchers developed information on the type, density, and location of T cells at the tumor sites and compared the predictive value of these data with information on a tumor's size and the extent to which it had spread to other tissues.

The density of T cells within a tumor was, in this population, a better predictor of patient survival than the tumor size and spread, which are typically used to develop prognoses, the researchers report in the September 29 Science.

Once the colorectal tumors become clinically detectable, the adaptive immune response may play a role in preventing tumor recurrence, the researchers say. "This suggests that the time to recurrence and overall survival time are governed in large part by the state of the local adaptive immune response," they write in Science.

In their analysis, a strong immune response was associated with a favorable prognosis regardless of the cancer size and spread; conversely, a weak immune response was associated with a very poor prognosis, even in patients whose tumors had not invaded other tissues.

"The recurrence of cancer may have little to do with the tumor itself - or at least not with tumor size and spread," notes Dr. Galon. "Rather, poor prognosis could arise from a weak immune reaction to cancer."

Patients whose tumors had high densities of certain T cells had a 5-year survival rate of 73 percent, compared with 30 percent for patients with low densities of T cells in tumor regions. In patients with earlier stage tumors, high densities of T cells were associated with a 79-percent chance of survival after 5 years, while patients with low densities had a 33-percent chance of survival.

The experimental methods used in the study are not ready for clinical use. But if the results are confirmed in larger studies, in theory the strategy could be used to identify patients who, because of their immune responses, are at high risk for relapse and may benefit from additional treatment.

"The immune system is the most important parameter to prevent relapse and metastasis and to prolong survival in colorectal cancer," notes Dr. Galon. The study was co-led by Dr. Franck Pagès, an immunologist at the European Georges Pompidou Hospital.

By Edward R. Winstead