Abstract
Among metastatic colorectal cancer patients with liver-dominant metastases, hepatic disease progression was reduced by 31% when selective internal radiation therapy (SIRT) was added to a FOLFOX-based first-line chemotherapy regimen. While overall PFS was not improved by adding SIRT, Ricky Sharma, MD, of Oxford University, the ASCO-designated discussant for the SIRFLOX trial, called the benefit “an impressive change in local control.” He cautioned that AEs were increased, however.
The international, multicenter, open-label, randomized controlled SIRFLOX trial enrolled chemotherapy-naïve patients with nonresectable liver-only, or liver-dominant (liver plus lung and/or lymph-node metastases) metastatic colorectal cancer. SIRT was delivered to the liver with yttrium-90 resin micro-spheres (Sirtex) via a hepatic artery injection. With Sirtex, liver tumors receive a single, large radiation dose over three weeks. The Food and Drug Administration (FDA) approved Sirtex for treatment of colorectal cancer liver metastases in 2002.
Dr. Gibbs noted that despite several decades of work with other liver-directed therapies, uncertainty remains about their clinical utility because large phase 3 randomized controlled trials are lacking. Liver metastases are the dominant disease site in metastatic colorectal cancer and the predominant cause of death. The combination of chemotherapy plus a biologic is standard first-line therapy for palliative treatment of metastatic colorectal cancer.
Patients in the two treatment arms received either modified (m) FOLFOX6 plus or minus bevacizumab (n = 263) or mFOLFOX6 plus Sirtex administered once with cycle 1 plus or minus bevacizumab until disease progression (n = 267). The primary endpoint was PFS. The presence of extrahepatic disease was one of the stratification factors. Patients’ mean age was 63 years; about a third were female. Forty percent had extrahepatic metastases, and about 90% had synchronous metastases. The primary tumor was removed in about 45% of patients.
Assessment of PFS at any site revealed no differences between groups (10.2 months for FOLFOX plus bevacizumab; 10.7 months for FOLFOX plus bevacizumab plus SIRT; P = 0.43). PFS in liver-dominant cases, however, was 12.6 months for FOLFOX plus bevacizumab and 20.5 months for FOLFOX plus bevacizumab plus SIRT (HR, 0.69; 95% CI, 0.55–0.90; P = 0.002), a 7.9-month improvement.
The ORR, although modestly higher overall for the SIRT arm (76.4% versus 68.1%; P = 0.113), was significantly higher in the liver (72.7% versus 66.9%; P = 0.042). In addition, the complete response rate overall displayed a trend for improvement in the SIRT-containing arm (4.5% versus 1.5%, P = 0.054), but in the liver was significantly higher (6.0% versus 1.9%; P = 0.020).
“Adverse events had no negative impact on duration of systemic therapy and were acceptable and as predicted,” Dr. Gibbs stated. Adverse events (grade 3 or higher) were significantly increased in the SIRT arm versus the FOLFOX plus or minus bevacizumab arm for neutropenia (40.7% versus 28.5%), febrile neutropenia (6.1% versus 1.9%), and thrombocytopenia (9.8% versus 2.6%). Gastric or duodenal ulcers and ascites were also higher for the SIRT group.
Dr. Sharma speculated that the failure to achieve an overall PFS advantage with Sirtex in SIRFLOX was likely attributable to inclusion of 40% of patients with extrahepatic disease. “But there is an impressive change in local control in the liver … so this is a robust result.”
Underscoring the need for more therapies, Dr. Sharma said that despite the FDA approval of 71 drugs for solid cancers between 2002 and 2014, improvements in median PFS and median OS have been only 2.5 and 2.1 months, respectively.