mohs or during their residencies.: 4 today, many mohs surgeons complete a fellowship after their dermatology residency, spending hundreds of hours observing and performing mohs surgery under careful supervision of highly experienced mohs surgeons. this is the most comprehensive and thorough method of learning mohs surgery. others learn the technique in their dermatology residencies and through courses and preceptorships. it is highly encouraged that a physician interested in learning mohs surgery should spend extended time observing, cutting, processing, and staining mohs specimens. it is vital that the histotechnologist prepare high quality slides. the histology block must be correctly mounted, cut, and stained the first time, as there is no second chance in mohs histology. it is not a procedure that can be properly mastered in a short period of time. comparison to other modalities of treatment pictogram of ccpdma or margin controlled histology pictogram of standard bread loafing histology false negative in standard bread loafing histology comparing mohs method to smashing an aluminum piepan how a mohs section is flattened with relaxing incisions mohs surgery is not suitable for all skin cancers. mohs micrographic surgery is the most reliable form of margin control; utilising a unique frozen section histology processing technique – allowing for the complete examination of 100% of the surgical margin. the method is unique in that it is a simple way to handle soft, hard-to-cut tissue. it is superior to serial bread loafing at a 0.1 mm interval for improved false negative error rate, requiring less time, tissue handling, and fewer glass slides mounted. the clinical quotes for cure rate of mohs surgery are from 97% to 99.8% after 5 years for newly diagnosed basal-cell cancer (bcc), decreasing to 94% or less for recurrent basal-cell cancer. radiation oncologists quote cure rates from 90 to 95% for bccs less than 1 or 2 cm, and 85 to 90% for bccs larger than 1 or 2 cm. the surgical excision cure rate varies from 90 to 95% for wide margins (4 to 6 mm) and small tumors, to as low as 70% for narrow margins and large tumors. society and culture some commentators argue that skin cancer surgery, including mohs surgery, is overutilised as rates of skin cancer surgery are increasing worldwide. it is unclear if this relates to higher rates of skin cancer, increased vigilance in diagnosis, and increased availability of the procedure, or patient and doctor preferences. the incidence of mohs surgery increased significantly over the decade between 2004 and 2014. in a sample of 100 mohs surgeries, the total cost ranged from us$474 to us$7,594, with the higher costs for hospital-based complex procedures. in australia, the direct out of pocket cost to patients may vary from $0 to $4000. when the non-mohs surgery is performed by multiple doctors including pathologists the costs may be increased further. this is especially true when the cancer is incompletely excised and requires repeat surgery. history originally, mohs used a chemical paste (an escharotic agent) to cauterize and kill the tissue. it was made of zinc chloride and bloodroot (the root of the plant sanguinaria canadensis, which contains the alkaloid sanguinarine). the original ingredients were 40.0 g stibnite, 10.0 g sanguinaria canadensis, and 34.5 ml of saturated zinc chloride solution.: 3–6 this paste is similar to black salve or "hoxsey's paste" (see hoxsey therapy), a fraudulent patent medicine, but its usage is different. hoxsey used the paste for long periods, a harmful practice that was rapidly discredited. mohs left the paste on the wound only overnight, and the following day, the cancer and surrounding skin would be anesthetized and the cancer removed. the specimen was then excised, and the tissue examined under the microscope. if cancer remained, more paste was applied, and the patient would return the following day. later, local anesthetic and frozen section histopathology applied to fresh tissue allowed the procedure to be performed the same day, with less tissue destruction, and similar cure rate.: 3–4