Early PET/CT superior to RECIST for tipping off long-term outcomes

Undergoing a pretreatment PET/CT scan has shown to have more predictive value than conventional follow-up protocol for colorectal cancer with metastases to the liver and could be the case for other cancers, according to a study published Oct. 17 in the Journal of Nuclear Medicine.

Secondo Lastoria, MD, from the nuclear medicine unit at Istituto Nazionale Tumori “Fondazione G. Pascale” IRCCS in Naples, Italy, and colleagues assessed the likely outcome of treatment for patients with resectable solid tumors of the liver, all metastatic colorectal cancer, by performing baseline and follow-up PET/CT scans for 33 patients undergoing one cycle of phase II preoperative FOLFIRI (folinic acid,  leucovorin, fluorouracil and irinotecan) chemotherapy with bevacizumab, an anti-angiogenesis drug. Researchers conducted quantitative PET/CT by calculating both maximum standardized uptake value (SUV) and total lesion glycolysis. Standard RECIST (Response Evaluation Criteria in Solid Tumors) CT protocol was used during follow-up three months after treatment. Both were compared to pathological response.

Results of the study showed that early metabolic PET/CT indications had more statistically significant predictive value for not only progression-free survival, but also overall survival of patients than RECIST and could strengthen the case for early PET/CT.

“The rapid readout of treatment effects that would allow prompt interruption of ineffective therapies and the possibility of proposing alternative options to patients is an extremely attractive perspective for tailoring healthcare,” wrote Lastoria et al.

Predictive PET/CT may be a more expensive alternative to RECIST, but researchers said the cost would be offset by the prevention of unnecessary treatment for patients predicted to have a poor response. Researchers referred to the use of PET/CT in this regard for lymphoma patients.

Subjects in this study were mostly men with a median age of 58 years and a baseline of 1-3 metastatic lesions of the liver, but five patients had four or more lesions. Baseline imaging was performed just days before the first cycle of chemotherapy. Before and after PET/CT scans were completed for all subjects, but treatment cycles differed in two patients who received not one, but two cycles of chemotherapy before follow-up PET/CT imaging. Looking at SUV values, there was obvious incongruence between PET/CT and RECIST, with PET/CT showing remarkable decreases in measurable parameters and more continuity between before and after results than RECIST and pathological response.

This study could further the use of early PET/CT has a predictive tool for treatment response and factor into the debate regarding the use of RECIST versus PET Response Criteria in Solid Tumors (PERCIST) and other prospective PET/CT protocols for the management of metastatic disease.  

“It would be important for clinical research and practice of oncology to identify effective surrogates for early prediction of success or failure of the ongoing treatment and eventually shift patients to alternative treatments,” wrote the authors. “Dimensional response is commonly used in research and practice, based on the principle that tumor shrinkage is a signal of treatment activity against cancer. After World Health Organization criteria, RECIST represents a highly refined method of response definition, with rules available for any possible case. However, its value as surrogate of long-term endpoints has been seldom validated and is largely criticized. On the other hand, there is no general agreement in the scientific community on the way PET/CT response could be assessed, notwithstanding guidelines of the European Organization for Research and Treatment of Cancer and the proposal of PET Response Criteria in Solid Tumors (PERCIST).”

Additional studies need to be conducted to validate early PET/CT as a tool for predicting post-treatment survival of metastatic colorectal and other cancers and to nail down how best to approach long-term outcomes of chemotherapy.