The data were presented by lead investigator Andrew S. Kennedy, M.D., F.A.C.R.O., Director, Radiation Oncology Research Sarah Cannon Research Institute, Nashville, TN.
SIR-Spheres microspheres are manufactured by Sirtex and are the only fully FDA PMA approved microsphere radiation therapy for the treatment of colorectal liver metastases. The microspheres are administered via the hepatic artery, either alone, or in conjunction with systemic chemotherapy.
“Our goal with these studies was to evaluate the overall survival, tumor response and safety of using microsphere therapy in patients who are no longer responding to chemotherapy,” said Dr. Kennedy. “Patients in the study had a history of heavy pre-treatment and presented challenges in finding an effective treatment option. These research findings should help to further define the role of SIRT in helping to shrink or control the tumors and prolong patient survival.”
Multi-Institutional U.S. Study Overview
This investigator initiated study was a retrospective analysis of the outcomes in 548 patients with metastatic colorectal cancer treated with SIR-Spheres microspheres from July 2002 to December 2011 at 11 U.S. institutions.1 All patients had received prior chemotherapy, with more than 30% having also received prior liver surgery or ablation.
The authors reported median survivals of 13.0, 9.0 and 8.1 months, respectively, in patients who had received 1, 2 or 3+ prior lines of chemotherapy. There were no significant differences in the adverse event profiles between the three groups. Most patients (97.8%) spent less than 24 hours in the hospital with the most common Grade 3 side effects being abdominal pain (7%) and fatigue (6%). The authors concluded that SIRT with SIR-Spheres microspheres appears to have a favorable risk/benefit ratio in patients with metastatic colorectal cancer who have failed chemotherapy. These data show a clinically relevant survival benefit in patients not responding to chemotherapy, including those who have been heavily pre-treated.
Independent Imaging Study Confirms Efficacy with SIRT
The second presentation from this study illustrated the response to SIRT therapy with SIR-Spheres microspheres from an imaging perspective.2 The study presented the results of an independent central review by a board-certified radiologist of 195 patients with metastatic colorectal cancer that were treated with SIR-Spheres microspheres and had measureable lesions at baseline and follow-up imaging. Tumor RECIST response at three months showed a Partial Response in 7.6% of patients, 47.3% experienced Stable Disease and 45.0% had Progressive Disease resulting in a Disease Control Rate of 55.0%. RECIST response at three months predicted median survival of 25.2 months in Partial Responders compared to 15.8 months in those with Stable Disease and 7.1 months with Progressive Disease.
Researchers noted that response to SIRT therapy at three months must be interpreted with caution due to the significant proportions of peri-tumoral edema and necrosis encountered. Both imaging findings may lead to either the underestimation of Partial Response/Stable Disease or the overestimation of Progressive Disease, respectively. Given these caveats, early hepatic radiological response to SIRT therapy appears to predict longer-term prognosis.
“These studies add to the growing body of scientific data further supporting the role of SIRT in treating metastatic colorectal cancer. In this specific patient population, the results compare favorably to many of recently approved chemotherapy and biologic agents, and provide another option to patients who may have stopped responding to systemic therapy,” said Mike Mangano, president of Sirtex Medical Inc. “It is our intention to continue to study SIR Spheres microspheres in various patient populations, with the goal of adding this treatment to conventional chemotherapy even earlier in the treatment algorithm. The SIRFLOX study, which is expected to complete enrollment in the first quarter of 2013, will test this hypothesis with the hope that controlling liver tumors will allow patients to live longer and experience an improved quality of life. We look forward to those results.”