Marker causes cancer cells to light up during surgery

Small tumors can be hard to spot during surgical removal. Often, surgeons cut away extra tissue, just to be on the safe side. A new fluorescent marker developed for ovarian cancer highlights which cells are cancerous, which makes more precise and complete removal of malignant tissue possible. To make ovarian tumors glow, scientists coupled a fluorescent molecule with folate, which is commonly known as vitamin B9. Because most cancers in the ovary express high levels of the receptor to which folate binds, the fluorescent conjugate attaches specifically to tumor cells.

Because humans are not capable to see the fluorescent glow with their own eyes, a special camera is used to opsonize the fluorescent marker for our eyes: the tumors glow white on a black background, as can be seen on the picture above. The same technique is used for fluorescence microscopy in the lab. For example, if scientists want to detect a specific cell type, they can mix a cell-specific fluorescent marker into their culture. The cells can then be seen on the microscope, which only shows the fluorescent signal coming from the label that has attached to the cells.

After the fluorescent probe has bound specifically to the cancerous cells, doctors can see them during surgery, improving excision of the malignant tissue. Apparently, the new method is highly precise: tissue as small as 50 micrometers can be detected during surgery. Such small tumors would not be visible if surgeons would simply rely on their eyesight.

The scientists have not yet shown that using the fluorescent marker actually improves the outcome of the surgery in patients. Clinical trials are needed to prove that opsonizing ovary tumors during surgery is beneficial for the patient. Although the researchers do not state so, the newly developed method could also serve as a template for a novel therapy to specifically kill cancer cells. Because the fluorescent cancer detector has already been tested in humans, and not just on a cell population in the lab, it is possible that doctors will soon gain access to fluorescent labels to assist them during surgery.

Specifically targeting cancer cells, either for opsonization by fluorescent markers, or to kill them with specialized "bullets" is something researchers have been trying for years. In some cases, it is possible specifically target cancer cells, but therapies where only the cancerous cells are targeted and killed are still sparse. In most cases, treatment involves antibodies that target molecules only found on cancer cells, coupled with a compound that is toxic for cells. One of the advantages of these so called "magic bullets" over regular chemotherapy is that specific targeting of cells reduces damage to healthy tissue, and thereby decreases side-effects.

Finding cancer-specific biomarkers and developing specialized "bullets" to target them will probably be the next standard for cancer treatment. Let's hope it replaces the crude and non-specific chemotherapeutic treatments that are still widely used.

NewScientist obtained a video showing off the labeling technique. The tumor cells in the video have been made green.

Update 2011-09-19 11.50: the University Medical Center in Groningen was the first hospital to use this technique; my home university. I just thought I'd mention that.