Confocal laser microscopy is a new technology enabling direct imaging of biological tissue to detect tumor subtypes with minimal tissue processing or damage. According to Kishwer S. Nehal, M.D., director of Mohs Micrographic Surgery at the Memorial Sloan-Kettering Cancer Center (New York, NY), the technology may be a useful tool for rapid, real-time imaging of skin-cancer tissue excised for margin assessment. The new procedure speeds up processing time and compares favorably with frozen tissue section analysis.
Mohs micrographic surgery entails the layer-by-layer microscopic examination and total removal of skin cancers, such as basal- and squamous-cell carcinomas, while minimizing the damage to healthy tissue. Performed on an outpatient basis, Mohs surgery can pinpoint cancerous areas otherwise invisible to the naked eye. After the skin is injected with a local anesthetic, the visible cancer and a very-thin layer of skin are removed with a scalpel, carefully mapped, and examined microscopically. If cancer is still seen under the microscope, another very-thin layer of skin is removed from that exact location. This may be repeated as often as necessary to completely remove the cancer.
Squamous-cell carcinoma, which most frequently occurs on sun-damaged skin, develops in 80,000 to 100,000 persons per year. According to the American Academy of Dermatology, the cure rate for squamous-cell carcinoma is 95% when properly treated. Because treatment delay can result in the development of large masses and tumor metastasis, 1200 people died of squamous-cell carcinoma in 1998, according to the American Cancer Society.
Basal-cell carcinoma, a common, sun-induced skin cancer, is usually treated by surgical removal. Accounting for more than 90% of all skin cancers in the USA (about one million cases per year), basal-cell carcinoma is often easily detected and has an excellent record for successful treatment by surgical removal. According to the American Academy of Dermatology, the cure rate for basal-cell carcinoma is 95% when properly treated. While this type of cancer rarely spreads to other parts of the body, it can extend below the skin to the bone and cause considerable local damage and can place people at high risk for developing additional skin cancers.
For the past year, Nehal has been examining tissue excised with Mohs surgery using confocal laser microscopy. She has performed the ex vivo confocal laser microscopy procedure using a diode laser from Lucid (Henrietta, NY) operating at 830 nm and has compared the results with those obtained by traditional microscopy techniques.
Twenty biopsy proven basal- and squamous-cell carcinomas excised with Mohs surgery were processed as frozen sections according to the Mohs technique, stained, and examined for the presence of tumors at the peripheral and deep surgical margins by traditional light microscopy. The corresponding tissue was then examined with the confocal laser microscope to determine whether surgical margins were clear. Ex vivo tissue was dipped in acetic acid to highlight the nuclei and provide contrast and placed in a cassette, which was inserted into the confocal imaging system. A computer monitor picture enabled Nehal to adjust the power of illumination, move the sample back and forth, and focus it in three dimensions. Laser light shining from below the sample provided the resolution and contrast to create a black and white image on the screen.
Then Nehal used the system to create a map as the system scanned over the tissue, providing a 750-mm field of view. The confocal images were compared to the traditional stained microscopic images to assess the accuracy detecting tumor subtypes by confocal laser microscopy. Tumors with large aggregates, such as nodular basal-cell carcinomas, were easily and consistently identified as an enhanced bright image with the confocal laser microscope.
"Confocal imaging can save time, as opposed to the freezing, cutting, and staining required for traditional microscopy," says Nehal. "We can scan in vivo and ex vivo tissue whenever we choose and obtain a brightly enhanced 3-D picture that is the equivalent of a tissue section 8 to 10 mm thick. We can see distinct properties that help us to understand what normal and diseased cells look like."
Source: Medical Laser Report, June 2001