Tumor excision: triple imaging for unique diagnostics

After their tumor has been removed, some patients have to return to the hospital to undergo surgery again. That's because the tumor was not precisely identified and was subsequently not completely removed. That's both an ethical and financial dilemma. A new surgery-adjacent procedure is designed to rapidly and accurately detect tumors.

In this MEDICA-tradefair.com interview, Professor Jürgen Popp explains why conventional frozen section biopsies often tend to overlook tumor tissue, describes the new diagnostic procedure and the three imaging techniques it combines and envisions the future of cancer care.

Professor Popp, what is the conventional surgical procedure for removing a tumor? How can this method be improved?

Prof. Jürgen Popp: To answer your question, I would like to focus on the head and neck area. It is relatively easy for surgeons to identify and remove a full-fledged tumor. It is much more problematic to identify tumor margins. What’s more, various environmental factors – including diet, alcohol consumption or smoking – often lead to inflammation surrounding the tumor in the head and neck area or other parts of the mucous membrane. This makes it more difficult to delineate them from a developing tumor. In most cases, surgeons resort to frozen section diagnostics. They take a biopsy, freeze it, cut it and stain it with hematoxylin and eosin (HE). However, there is a high probability that we overlook or miss tumor tissue with this traditional frozen section procedure. That's because when it comes to frozen material, the quality of this type of staining is not as good the quality of histological stains. For the latter, the biopsy is embedded in formalin before it is cut and stained. Embedding biopsies in formalin renders entirely different and better stain results. Having said that, a biopsy has to first be sent to the lab for analysis by a pathologist, which typically takes between two to eight days. Unfortunately, this means that between 15 and 20 percent of patients have to return to the hospital after tumor removal because more tumor tissue was subsequently detected. Needless to say, this is a considerable psychological burden on patients. Another concern is scar tissue that forms within one to two weeks after the first surgery, which makes tumor localization even more difficult. That’s why we need a rapid analysis method with the lowest possible error rate.

You were able to develop this type of procedure. How does it work?

Popp: This is a so-called multimodal approach. After we have taken the biopsy, frozen and cut it, we examine the individual sections under a multimodal microscope. Thanks to short-pulse lasers, we are able to immediately provide the clinician with the key information. We combine three imaging techniques to create different morphological, chemical or biochemical contrasts. The first imaging technique is called coherent anti-Stokes Raman scattering and allows us to produce molecular contrast and show the distribution of lipids, proteins or DNA. The second method is two-photon fluorescence microscopy, which illustrates the distribution of certain enzymes. Flavins such as FAD tend to be increased in tumors or tumor margins for example. The third contrast mechanism involves second-harmonic imaging microscopy, which enables us to make collagen visible. Collagen surrounds tumor tissue and is responsible for cellular stiffness. The three methods combined create a multimodal image we can analyze and interpret accordingly.

How does this interpretation process work? How do you assess these images?

Popp: Basically, we take two approaches. The first approach uses artificial intelligence, allowing us along with the pathologist to delineate between healthy and diseased areas. This enables us to accurately identify the tumor margins.

We translate the multimodal image into histochemical stains with the second assessment technique. Unlike frozen section biopsy or pathology, there is no need for us to stain the sections. We can calculate an H&E stained image using our multimodal image. In other words, the pathologist doesn't even have to be on-site to examine the tissue, identify the tumor or tumor margin and determine where the tissue is healthy, free of cancer cells, or still affected. This is made possible by telemedicine services. It allows the surgeon to act immediately and cut away the respective tissue. Both are ex vivo methods we are currently pursuing.

What other possibilities does this technology open up apart from the ex vivo diagnostic setting?

Popp: We presently don't use this approach on the patient, but use it as a complement to the surgery. Having said that, our long-term goal is to eliminate the need for taking a biopsy from the patient's body and using the method in vivo. The idea is for the surgeon to enter the affected area using a probe to delineate between healthy and diseased tissue. However, we still have to hone the procedure's probe and penetration depth.

Our other vision is to use the technology not only for diagnostic purposes but as a treatment approach where we use a CO₂ laser to remove the tumor immediately after it has been identified. Yet another idea is to eliminate the need for cutting out the tumor with the laser and using ablation instead. In this case, the tumor is removed layer by layer. But it requires further extensive research in these areas.

What's your prediction for what cancer care will look like ten years from now?

Popp: The number of cancer patients will definitely increase in the future. Since the world population is growing and aging, there will also be increased incidences of cancer. This results in a growing demand for diagnostic examinations and treatment. Our current methods won't be sufficient when this day comes. This is where we are tasked with becoming faster and more efficient, and that is why our technique looks promising. We hope that there will be an increase in optical techniques to monitor different types of tumors – including tumors in the head and neck area, brain tumors, bladder and prostate cancer, colon cancer etc. Whether or not this will someday be possible by using both ex vivo and in vivo diagnostics is primarily a question of available funding. Research already focuses on this subject. The latest trends show that we are headed in this direction.