Real-time fluorescence imaging in intraoperative decision making for cancer surgery

5-Aminolevulinic acid is a non-fluorescent prodrug that leads to intracellular accumulation of fluorescent porphyrins in malignant gliomas-a finding that is under investigation for intraoperative identification and resection of these tumours. We aimed to assess the effect of fluorescence-guided resection with 5-aminolevulinic acid on surgical radicality, progression-free survival, overall survival, and morbidity. 322 patients aged 23-73 years with suspected malignant glioma amenable to complete resection of contrast-enhancing tumour were randomly assigned to 20 mg/kg bodyweight 5-aminolevulinic acid for fluorescence-guided resection (n=161) or to conventional microsurgery with white light (n=161). The primary endpoints were the number of patients without contrast-enhancing tumour on early MRI (ie, that obtained within 72 h after surgery) and 6-month progression-free survival as assessed by MRI. Secondary endpoints were volume of residual tumour on postoperative MRI, overall survival, neurological deficit, and toxic effects. We report the results of an interim analysis with 270 patients in the full-analysis population (139 assigned 5-aminolevulinic acid, 131 assigned white light), which excluded patients with ineligible histological and radiological findings as assessed by central reviewers who were masked as to treatment allocation; the interim analysis resulted in termination of the study as defined by the protocol. Primary and secondary endpoints were analysed by intention to treat in the full-analysis population. The study is registered at http://www.clinicaltrials.gov as NCT00241670. Median follow-up was 35.4 months (95% CI 1.0-56.7). Contrast-enhancing tumour was resected completely in 90 (65%) of 139 patients assigned 5-aminolevulinic acid compared with 47 (36%) of 131 assigned white light (difference between groups 29% [95% CI 17-40], p<0.0001). Patients allocated 5-aminolevulinic acid had higher 6-month progression free survival than did those allocated white light (41.0% [32.8-49.2] vs 21.1% [14.0-28.2]; difference between groups 19.9% [9.1-30.7], p=0.0003, Z test). Groups did not differ in the frequency of severe adverse events or adverse events in any organ system class reported within 7 days after surgery. Tumour fluorescence derived from 5-aminolevulinic acid enables more complete resections of contrast-enhancing tumour, leading to improved progression-free survival in patients with malignant glioma.

There is still no general consensus in the literature regarding the role of extent of glioma resection in improving patient outcome. Although the importance of resection in obtaining tissue diagnosis and alleviating symptoms is clear, a lack of Class I evidence prevents similar certainty in assessing the influence of extent of resection. We reviewed every major clinical publication since 1990 on the role of extent of resection in glioma outcome. Twenty-eight high-grade glioma articles and 10 low-grade glioma articles were examined in terms of quality of evidence, expected extent of resection, and survival benefit. Despite persistent limitations in the quality of data, mounting evidence suggests that more extensive surgical resection is associated with longer life expectancy for both low- and high-grade gliomas.

Paradigm shifts in surgery arise when surgeons are empowered to perform surgery faster, better and less expensively than current standards. Optical imaging that exploits invisible near-infrared (NIR) fluorescent light (700-900 nm) has the potential to improve cancer surgery outcomes, minimize the time patients are under anaesthesia and lower health-care costs largely by way of its improved contrast and depth of tissue penetration relative to visible light. Accordingly, the past few years have witnessed an explosion of proof-of-concept clinical trials in the field. In this Review, we introduce the concept of NIR fluorescence imaging for cancer surgery, examine the clinical trial literature to date and outline the key issues pertaining to imaging system and contrast agent optimization. Although NIR seems to be superior to many traditional imaging techniques, its incorporation into routine care of patients with cancer depends on rigorous clinical trials and validation studies.