Mohs Micrographic Surgery Section of Specimens Using Cryostat, Stain, and Immunostain

The key advantages of Mohs micrographic surgery (MMS) include precise microscopic control of tumor margins through specialized tissue processing techniques and the conservation of healthy tissue. Please see StatPearls' companion resource, "Mohs Micrographic Surgery," for more information. A complete margin assessment requires high-quality frozen sections free from processing errors that could impede the surgeon's ability to accurately examine the tumor. Inadequate techniques may result in improper staining, misorientation of margins, misinterpretation of tumor margins, and loss of critical tumor characteristics. Ultimately, these issues can lead to patient harm, suboptimal postoperative management, increased risk of disease recurrence, and higher costs. The technique for creating frozen sections and staining (including immunostaining) in MMS is similar to other forms of pathological sectioning and staining. However, Mohs surgeons and histology technicians use various methods for processing. The tissue is prepared to allow for the assessment of 100% of the peripheral and deep margins in a single section. This is accomplished by manipulating the excised specimen to ensure that the peripheral and deep margins lie in the same plane, mounting the specimen on a chuck for sectioning, and using a cryostat to freeze the tissue and cut frozen sections with a microtome blade. Staining is performed after the specimen is cut on the microtome and transferred to a glass slide. Hematoxylin and eosin (H&E) staining is the most commonly used method in MMS. Toluidine blue is used less frequently and is primarily applied when treating basal cell carcinomas (BCCs). Immunohistochemistry is mainly utilized for melanomas, with the melanoma antigen recognized by T cells (MART-1) stain being the most common in MMS. Other immunohistochemistry stains for melanoma include SOX10, PRAME, HMB-45, MEL-5, and S100. While immunostaining with cytokeratins can be helpful for detecting BCCs and squamous cell carcinomas (SCCs), few surgeons use this method due to the increased time and cost involved. Reports have indicated that cytokeratin stains can be useful for confirming perineural invasion in SCCs and BCCs. When interpreting slides, surgeons should note any changes in slide quality resulting from processing errors and devise strategies to address these issues. This plan must be communicated to the entire team, particularly the histology technicians. Common findings associated with processing errors include tears or holes in tissue sections, excessive or minimal staining, bubbles, and water beads. Prompt recognition of these issues is crucial, as it enables the team to identify the most appropriate troubleshooting techniques to resolve the processing errors.