EXPERT ANALYSIS FROM WCD 2015
VANCOUVER (FRONTLINE MEDICAL NEWS) – Investigators at the Memorial Sloan Kettering Skin Cancer Center in Hauppauge, N.Y. have found a simple solution for a vexing problem in Mohs surgery, histology sections that don’t fully stain with toluidine blue.
The problem, it turns out, is that aluminum chloride and Monsel’s solution (ferric subsulfate) – common topical hemostatics used during the procedure – block the stain from binding tissue. Washing sections in ethylenediaminetetraacetic acid (EDTA) before staining completely eliminates the problem .
“I think this will be very useful for Mohs surgeons. It’s a very simple step, a simple modification of routine staining protocol that [eradicates] this type of artifact. When technicians collect the specimen onto the slide, they wash it with EDTA solution for about 10 seconds.” Toluidine blue staining afterward “will be perfect. There won’t be any artifact,” said senior investigator Dr. Chih-Shan Jason Chen, director of dermatologic surgery at the Hauppauge center.
It’s an important finding (and one not yet published in the medical literature, according to Dr. Chen) because staining artifacts make it impossible to read toluidine blue sections with confidence, so Mohs surgeons have to go back and take more sections, creating a deeper wound.
Over a period of the past 2 years, the EDTA wash “has made a significant difference in my practice. I never see this type of artifact anymore. I can be very comfortable taking a very thin layer of tissue and don’t need to take extra stages. We don’t need to do fancy reconstructive surgery” for the wound to heal. “This process fits with the spirit of Mohs surgery, the concept of tissue conservation,” Dr. Chen said at the World Congress of Dermatology.
Perhaps about 20% of Mohs surgeons rely heavily on toluidine blue, especially to stain for basal cell carcinomas. “The nests of cancer cells are very small, so if you have an artifact, you are going to miss them,” he noted.
The first clue that hemostatic agents were to blame was that the artifacts didn’t occur with the first Mohs cut, but only in second and subsequent sections after hemostatic agents had been applied, and especially in thinner sections more permeable to those agents. Dr. Chen tried the EDTA wash, and it worked.
His research assistant, Curtis Chen, an incoming medical student at the University of Miami, figured out the chemistry. Aluminum and iron cations from the agents bind the tissue sample, inhibiting adherence of toluidine blue. EDTA, a chelating agent, scavenges the ions, releasing the tissue for staining.
Dr. Chen and Mr. Chen had no relevant financial disclosures, and there was no outside funding for the work.