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ADVANCED TECHNIQUES IN MOHS MICROGRAPHIC SURGERY
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Micrographic surgeons must have a working knowledge of pathology techniques including immunohistochemical stains and newly developed and developing molecular diagnostics.
From a practical standpoint, with the exception of lentigo maligna (and potentially superficially invasive melanomas), there are few tumors that benefit from the addition of frozen section immunohistochemistry at the time of micrographic surgery.
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Beginner Pearls
Maintain regular contact with colleagues in dermatopathology. The perspective of the pathologist and surgeon must be mutually understood.
Personal visits are better than phone calls which are better than e-mails which are better than text messages.
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Expert Pearls
Poorly differentiated tumor cells, dense inflammation, perineural invasion, and fibrosis are all situations in which immunohistochemical stains may be useful. The most widely used is AE1/AE3, a pan-keratin marker, which will label most carcinomas.
If there is specific concern for BCC, a Ber-EP4 stain can be performed.
CK7 for EMPD may be helpful in Mohs frozen sections. The main caveat to using this stain is the usually large sizes of the pieces of tissue to be examined in EMPD.
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Don’t Forget!
New terms are introduced into the literature by both clinicians and pathologists in an attempt to better define pathological entities and stratify risk. In recent years, the terms atypical intradermal smooth muscle neoplasm (instead of cutaneous leiomyosarcoma) and pleomorphic dermal sarcoma/undifferentiated pleomorphic sarcoma have been introduced. Pleomorphic dermal sarcoma/undifferentiated pleomorphic sarcoma is a distinct entity from AFX and has a worse prognosis.
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Pitfalls and Cautions
CD34 as a frozen section immunohistochemical stain for DFSP treated by MMS is discouraged. The nonspecific background staining, as well as the labeling of endothelial cells, makes this extremely difficult to interpret on frozen section pathology.
Some tumors may also benefit from adjuvant therapy, such as postoperative radiation.
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Patient Education Points
Patients should be explained that many rarer or more aggressive tumors have a high defect to lesion ratio, so an ostensibly small tumor may end up leading to a very large defect.
The high cure rates cited for Mohs surgery are generally applicable to primary low-risk tumors; tumors with negative prognostic factors (infiltrative or perineural patterns) or unusual tumor types (Merkel cell carcinoma, DFSP) may be associated with significantly higher recurrence rates.
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Billing Pearls
Billing for immunohistochemical stains is in addition to standard Mohs layer billing, and is generally billed on a per-specimen basis with code 88342 for the first antibody followed by 88341 for each additional antibody. If multiple separately identifiable antibodies are applied to the slide, use one unit of 88344.
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Even in the busiest Mohs micrographic surgery (MMS) practice or at a tertiary/quaternary referral center, special stains are not used on a frequent basis. Treating these cases not only requires a technically proficient micrographic surgeon and laboratory, ...