To improve staging, debulking, and prognosis in cytoreductive surgery, researchers at the University of Groningen in the Netherlands and the Technische Universität München & Helmholtz Zentrum in Germany have developed a fluorescence imaging technique to visualize ovarian tumors (doi:10.1038/nm.2472). Professor Gooitzen M van Dam and colleagues have investigated the intraoperative tumor-specific fluorescence imaging in ovarian cancer. The promising results of the first in-human use of the real-time tumor-specific visualization technique are reported online ahead of print this week in Nature Medicine. In a small patient cohort, the technique was found to be safe, and the ligand-fluorescent dye is so far nontoxic, inexpensive, and relatively easy to create.
The Rationale for Real-Time Tumor Imaging During Surgery
The overexpression of folate receptor-α (FR-α) in 90% to 95% of epithelial ovarian cancers and lack of FR-α in healthy cells prompted the investigators to create an intraoperative tumor-specific fluorescence imaging system for ovarian cancer surgery. In the study, the ligand for FR-α, folate, was conjugated to fluorescein(Drug information on fluorescein) isothiocyanate (folate-FITC) which then binds FR-α. The fluorescent dye conjugated to folate is injected intravenously two hours before surgery. The fluorescent ligand-receptor is then visualized using a real-time multispectral intraoperative fluorescence imaging system to facilitate fine-tuned and radical cytoreduction as all tumor cells can now be directly visualized in detail. “Fluorescence imaging, as an optical technique, relates naturally to surgical inspection and practice, and it offers superior resolution and sensitivity compared to preoperative radiological imaging and to visual inspection and palpation during surgery,” the authors explain.
The development of the technique was prompted by the difficulty in determining the precise borders of a tumor during debulking surgery. Because epithelial ovarian cancer (EOC) has no distinctive clinical presentation in early stage, the majority of EOCs are diagnosed in advanced stages when cytoreduction and chemotherapy are seen as the most effective form of first-line treatment. Ovarian cancer remains the most frequent cause of death of all gynecological cancers with the extent of cytoreduction as a prognosis factor that is actively influenced by the surgeon. Tumor-specific imaging during surgery could greatly improve cytoreductive techniques by the removal of residual tumor tissue that cannot be seen by the naked eye.
“The technology development of the camera and the tracer took place several years ago," said associate Professor van Dam. "The tracer was developed and tested in mice at the University of Purdue by Professor Low while the camera has been developed by Professor Ntziachristos in Harvard initially in 2007 and later on he continued with it at the Technical University of Munich in Germany." The practice was put in to clinical use at the University of Groningen at the end of 2008. The first patient was imaged in 2009.
The team is also working on two other tracers in order to also cover those patients that do not express FR-α, and they anticipate the first results by the end of 2012, according to professor van Dam.
The clinical team found that the fluorescent compound was safe to patients and allowed precise and specific tumor visualization to determine tumor stage and the extent of tumor spreading. The imaging technique was used on four patients with malignant EOCs and five patients with benign ovarian tumors. Fluorescence was detected in 3 of 4 malignant ovarian cancer patients as one patient had no FR-α expression. No fluorescence was detected in patients with benign tumors. Healthy tissue did not exhibit any fluorescence in vivo or ex vivo nor did the imaging system interfere with surgery performance. Tumor tissue was confirmed ex vivo by histopathology.
The surgical clinicians reported the ability to excise fluorescent tumor deposits that were less than 1 mm thanks to the real-time image-guiding system. Fluorescence was detected from 2 hours and up to 8 hours after injection during a long surgical procedure. The number of tumorous regions detected by surgeons using the fluorescent-guided technique was significantly higher than with visual observation alone (median of 34 regions using fluorescence compared with 7 by naked-eye visualization). The authors report that the “results show excellent correlation with the presence and intensity of the intraoperative fluorescence signal.”
Professor van Dam highlighted the collaborative effort it took to achieve these results. “It is a truly multidisciplinary achievement in which every component is as important as the other one. It is a technology developed not by merely one center but by a collaboration of three institutions: Technical University of Munich, Purdue University, and the University of Groningen.”
Future studies and application
Because not all patients’ tumors express FR-α, FR-α detection via tumor tissue obtained during a staging laparoscopy or primary surgery or a preoperative folate-targeted technetium scan could be used to identify patients suitable for FR-α targeted image-guided surgery. Determining the amount of residual tumor tissue during interval debulking is crucial in order to remove residual disease. As a greater number of ovarian cancer patients are being treated with neoadjuvant chemotherapy, it is also important to determine whether post-chemotherapy tumor cells continue to express the folate receptor. A recent study that will be published in Cell Oncology (Crane et al, in press) has shown that 350 patients continue to express the receptor following chemotherapy, supporting the use of the folate-FITC imaging technique regardless of prior chemotherapy treatment.
Larger, multicenter and international patient cohort follow-up studies will better determine both the diagnostic and outcome value of this technique. Potentially, major advantages are the decrease of further surgical interventions, decreased morbidities, and better cytoreduction and the improvement of the effect of subsequent chemotherapy because of the decreased tumor burden. With further development, precise real-time, fluorescent tumor imaging could result in a paradigm shift of improved staging and cytoreduction value leading to better patient outcomes and post-surgical prognoses. “We envision a dramatic change within the next 3 to 5 years taking into the consideration the necessary phase II and III studies,” explained van Dam.
CancerNetwork spoke to Professor van Dam about the development of this imaging technology to other cancer types. The University of Groningen, together with the Technical University of Munich are also now developing camera systems for laparoscopy and endoscopy (ie colonoscopy and gastroduodenoscopy). "It is important to realize that for each type of tumor you need to know which tumor marker is upregulated and most prevalent," noted van Dam.
The researchers have developed an assay to test on biopsies of patients with ovarian, colorectal, or gastric cancers to determine which tumor marker is expressed the highest on the surface of the cell. "This way we can use an optical tracer for that specific marker. We are now in the process of testing several other tracers besides the one for ovarian cancer—for breast cancer, colorectal cancer, prostate cancer, and gastric cancer." Van Dam anticipates that following necessary phase II studies to test for diagnostic accuracy, the technology will become widely available for other surgeons in the field because of the easy-to-perform aspect of the technology. "We are now working with other centers in the Netherlands and the US to move as fast forward as possible to make this available to the larger population.”