Trying to predict whether or not chemotherapy was working as soon as possible, Swedish doctors compared FDG-PET scanning before beginning chemo and after two treatments. Then they looked at CT scans after four and eight treatments to see if early PET scans could predict changes in tumor size.
They found that the scans did show which patients would respond to treatments with tumor shrinkage. Responders had greater reduction in metabolic readings on PET scans than did patients whose tumors didn’t get smaller. But changes in PET values did not predict benefits in either the time until cancer got worse (progression-free interval) or overall survival.
Patients who responded to chemotherapy with tumor shrinkage had the lowest standard uptake values (SUVs) on PET scans before chemotherapy began. Non-responders showed higher metabolism within tumors on PET before chemotherapy.
Dr. P. Byström and colleagues at the Karolinska Institute in Stockholm concluded,
Although metabolic response assessed by FDG-PET reflects radiological tumor volume changes, the sensitivity and specificity are too low to support the routine use of PET in metastatic colorectal cancer. Furthermore, PET failed to reflect long-term outcome and can, thus, not be used as surrogate end point for hard endpoint benefit.
SOURCE: Bystrom et al., Annals of Oncology, Volume 20, Number 6, June 2009.
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