MONDAY, Nov. 24 (HealthDay News) -- A transfusion of fresh red blood cells -- emphasis on the word "fresh" -- may help cancer patients better avoid cancer recurrence and improve their odds of long-term survival, a new report suggests.

The study, presented in the December issue of Anesthesiology, is based on research into the mystery of why blood transfusions during certain cancer surgeries appeared to have the opposite effect -- increased cancer recurrence and reduced survival rates.

In tests done on rat models of leukemia and breast cancer, researchers from Tel Aviv University found a blood transfusion does hurt the odds but only if the blood used had been stored for nine days or more.

A study by Shamgar Ben-Eliyahu and his research group, however, offers unique and surprising insights that could open doors for important research in humans in the near future.

"The results of our study clearly indicate that blood transfusion is an independent risk factor for cancer recurrence in the animal models we used," Ben-Eliyahu said in a news release issued by the journal's publisher. "But our study also yielded two surprising findings. First, the storage time of the transfused blood was the critical determinant of harmful effects: fresh blood had no harmful effects. Second, and even more surprising, we found that red blood cells, not white blood cells, caused the effects we observed."

Previously, the white blood cells in transfused blood had been widely thought to cause any harmful effects of a transfusion, he said.

"The current common approach in cancer patients is to use transfused blood depleted of white blood cells," Ben-Eliyahu said. "But we found that removal of white blood cells was ineffective in our setting."

He called for more studies in cancer patients to determine if changes in blood transfusion practices can improve patient outcomes.

More information

The Nemours Foundation has more about blood transfusions.