When radioactive beads are injected into the artery feeding the livers of colorectal cancer patients, the time before liver tumors get worse increases, as well as the time to overall cancer progression in the body.
In a process called radioembolization, resin beads loaded with yttrium-90, a radioactive isotope, are injected directly to the large artery leading to the liver (hepatic artery). They travel to the tiny blood vessels around liver tumors and emit radiation for about 14 days.
Because tumors receive their blood supply primarily through the hepatic artery while healthy liver receives blood through the portal vein, healthy liver tissue is spared radiation.
The yttrium-90 radioembolization treatment is known as selective internal radiation therapy(SIRT) or SIR-Spheres.
Scientists compared protracted 14 day infusions of 5-FU alone to the same infusions plus an inital treatment with radioactive yttrium-90 beads. Forty-six patients were randomly assigned to either 3-week cycles of protracted 5-FU until their cancer got worse or side effects were intolerable or one SIR-Spheres treatment followed by cycles of protracted 5-FU.
Patients in the 5-FU only arm of the trial were allowed to cross over and receive SIR-Spheres after their cancer progressed. Ten patients crossed over and got radioembolization.
Patients who were part of the trials had refractory colorectal cancer — their tumors had gotten worse on all standard treatments. They couldn’t have tumors outside their liver (extrahepatic disease).
The goal was to find out if treatment with resin beads carrying radioactive yttrium could increase the time before cancer progressed in the liver or elsewhere in the body. The researchers also measured tumor shrinkage (response), time to cancer progression anywhere in the body, and overall survival time after the treatment began.
- Time to cancer progression in the liver was 2.1 months on 5-FU alone and 5.5 months with yttrium-resin microspheres.
- Time to progression anywhere in the body was 2.1 months on 5-FU only and 4.5 months with the microspheres.
Survival time was 7.3 months for the 5-FU arm and 10 months with microspheres, but this was not statistically significant. Crossovers and additional treatments made it difficult to decide on the impact of Yttrium-resin beads on survival.
Alain Hendlisz and colleagues concluded,
Radioembolization with 90Y-resin microspheres plus FU is well tolerated and significantly improves time to liver progression and time to progression compared with FU alone. This procedure is a valid therapeutic option for chemotherapy-refractory liver-limited metastatic colorectal cancer.