When is Mohs Micrographic Surgery Appropriate?
Thursday, October 13, 2011
Mohs micrographic surgery (MMS) is an elegant treatment that
allows the physician to fulfill two roles simultaneously - those of
the surgeon and the pathologist. Fellowship-trained Mohs surgeons
have received significant education in oncology, surgery,
dermatopathology and reconstructive techniques. MMS entails staged
excisional removal, margin evaluation of en face frozen sections
with tumor mapping, and reconstruction following tumor
Such microscopic control of surgical margins affords MMS the
highest cure rates for cutaneous malignancy and, given the smaller
margins typically used, affords preservation of the maximum amount
of healthy tissue.1 Smaller post-operative defects,
combined with the knowledge of clear margins at the time of
reconstruction, give the Mohs surgeon a distinct advantage,
particularly for tumors in cosmetically sensitive areas.
Despite these advantages, MMS might prove to be inconvenient for
patients who do not have a Mohs surgeon within a reasonable travel
distance. Furthermore, MMS can be a lengthy procedure that might
prove too difficult for patients with certain physical or
psychiatric comorbidities. Finally, although MMS is
cost-effective,2 it has been placed under increased
scrutiny from insurers. In addition to doing what is appropriate
for our patients, we have to be good financial stewards of the
healthcare dollar. From these perspectives, we now find ourselves
asking the question - when is MMS appropriate?
When is MMS an option?
Standard surgical excision remains a mainstay of treatment for
many cases of low-risk, primary cutaneous malignancy; indeed,
excision with 5-6 mm margins can achieve cure rates in the 90
percentile range.3 A large meta-analysis of
retrospective studies showed that the 5-year recurrence rate for
surgical excision of primary basal cell carcinoma (BCC) is
10.1%.4 Surgical excision or destructive procedures are
often sufficient for many low-risk BCCs, providing convenience and
cost efficacy. However, when risk of recurrence is high, as will be
discussed in this article, MMS remains the preferred treatment
choice given its superior cure rates.5
MMS depends upon contiguous tumor growth, albeit often
asymmetric and subclinical. Many tumor types share these basic
characteristics that make them amenable to treatment with MMS
(Figures 1-3). Common among these are BCC, squamous cell carcinoma
(SCC) and melanoma in situ. More uncommon tumors, such as
dermatofibrosarcoma protuberans, atypical fibroxanthoma, sebaceous
carcinoma, microcystic adenexal carcinoma and extramammary Paget's
disease, are also frequently treated with MMS owing to their growth
pattern and sometimes stubborn nature.
Figure 1. Preoperative appearance of a "typical" BCC on
the cheek (note the smaller BCC on the nasal ala).
BCC is the most common form of skin cancer. Management of these
tumors is generally straightforward, but not all tumors are created
equally. A lesion's biological behavior might vary based on
subtype, size, anatomic location, and histologic
features.5 When considering the treatment of BCC,
well-accepted indications for MMS are those tumor characteristics
that predispose to a higher recurrence rate. These include
high-risk site (central face, near the eye, nose, lips, and ears);
tumor size (>2cm, or >1cm on non-mask areas of the face);
histologic subtype (morpheaform, infiltrative, micronodular, and
basosquamous); clinically indistinct margins; recurrent lesions;
and perineural or perivascular involvement.6
Several other factors that might be associated with more
aggressive behavior should be considered, such as history of
radiation, immune-compromised status, evolution in a previous scar,
or positive margins on excision.
MMS is often the treatment of choice for SCC, for which
recurrence risk is also high. Specifically, perineural invasion is
associated with high-risk lesions, and MMS allows the surgeon to
track perineural involvement until clearance is achieved or a
cranial foramen is reached.7
Figure 2. Despite its initial appearance, this tumor had
significant subclinical spread and required multiple stages of Mohs
with this resultant defect.
In addition to having lower recurrence rates, MMS is often
touted as a tissue-sparing technique. Studies suggest that excision
of a small (<20 mm) BCC with a 3 mm margin will result in a cure
in 85% of cases. With a 4-5 mm margin, the clearance rate rises to
nearly 95%. These data indicate that 5% of small, well-defined BCCs
extend over 4 mm beyond the clinical margin.3,8 In a
randomized controlled trial in 2009, Muller et al.1
compared post-operative defect sizes following surgical excision
with 4 mm margins and after MMS. They found that the median area of
the defect from surgical excision was 1.6 times larger than that of
MMS.1 Smaller defects have obvious advantages in terms
of reconstruction, and could conceivably lead to improved
functional and cosmetic outcomes, as well as theoretical cost
Figure 3. One-week post-repair, which utilized a large
rotation flap (i.e., Mustarde flap) on the cheek and transposition
flap on the ala).
Melanoma in situ
The role of MMS in malignant melanoma is controversial, but has
been better established in melanoma in situ and lentigo
maligna. These lesions frequently occur in significantly
sun-damaged skin where there can be a significant background of
atypical melanocytes; this makes margin determination difficult
both clinically and histologically. Excision with microscopic
margin control, as with MMS, has value in this setting to help
avoid potential recurrence/re-excision or unnecessarily large
margins. Although melanocytic lesions can be difficult to evaluate
using frozen sections, the use of rapid immunohistochemistry
staining protocols allows for such tumors to be treated with
MMS can also play a role in the treatment of rare, infiltrative
tumors such as dermatofibrosarcoma protuberans (DFSP) and atypical
fibroxanthoma (AFX). Traditionally, these tumors have been treated
with wide local excision. However, the resulting defects can be
quite large; MMS has been shown to enhance cure rates and might
help to simplify reconstruction and limit patient morbidity.
For DFSP, recurrence rates are much improved with MMS (1.5%)
over wide local excision (>2 cm margin; 8.8%) or conservative
excision with undefined margins (39.57%).9,10 With
regard to AFX, studies suggest that wide local excision with a 2 cm
margin is required to achieve complete tumor clearance in 96.6% of
cases. However, the majority of these tumors could be cleared using
MMS with much smaller margins (5 mm), therefore making a strong
case for the use of MMS.11,12
Therapeutic guidelines aim to aid selection of the most
appropriate treatment for individual patients, but the management
of cutaneous malignancies is complex. Truthfully, guidelines only
exist where the clear path is not obvious. Characteristics of both
the tumor and the patient are equally important in determining what
is the best treatment for a given skin cancer. Although many
malignancies can be treated effectively with MMS, non-melanoma skin
cancers are most common.
Tumor characteristics that predispose to a higher risk of
recurrence - such as tumor type, subtype, location, size,
clinically indistinct margins, history of recurrence, and
histologic features (mitotic rate, pleomorphism, and
perineural/perivascular involvement) - might steer decision-making
towards MMS. In addition, comorbidities, convenience, cosmetic
outcome, expected severity of a possible recurrence, and patient
preference also influence the therapeutic decision for an
individual patient. The decision of whether to employ MMS is best
made on a case-by-case basis by an experienced practitioner or
surgeon (see Table 1).
Table 1. Appropriate indications for Mohs
- Muller FM, Dawe RS, Moseley H, Fleming CJ. Randomized
comparison of Mohs micrographic surgery and surgical excision for
small nodular basal cell carcinoma: tissue-sparing outcome.
Dermatol Surg 2009;35:1349-1354.
- Cook J, Zitelli JA. Mohs micrographic surgery: a cost analysis.
J Am Acad Dermatol 1998;39:698-703.
- Wolf DJ, Zitelli JA. Surgical margins for basal cell carcinoma.
Arch Dermatol 1987;123:340-344.
- Rowe DE, Carroll RF, Day CL. Long-term recurrence rates in
previously untreated (primary) basal cell carcinoma: implications
for patient follow-up. J Dermatol Surg Oncol
- Minton TJ. Contemporary Mohs surgery applications. Curr
Opin Otolaryngol Head Neck Surg 2008;16:376-380.
- Tefler NR, Colver GB, Bowers PW. Guidelines for the management
of basal cell carcinoma. Br J Dermatol
- Perkins W. Who should have Mohs micrographic surgery? Curr
Opin OtolaryngolHead Neck Surg 2010;18:283-289.
- Kimyai-Asadi A, Goldberg LH, Peterson SR, et al.
Efficacy of narrow-margin excision of well-demarcated primary
facial basal cell carcinomas. J Am Acad Dermatol
- Lemm D, Mugge LO, Mentzel T, Hoffken K. Current treatment
options in dermatofibrosarcoma protuberans. J Cancer
Res Clin Oncol 2009;135:653-665.
- Paradisi A, Abeni D, Rusciani A, et al.
Dermatofibrosarcoma protuberans: wide local excision vs. Mohs
micrographic surgery. Cancer Treatment Rev
- Wollina U, Schonlebe J, Koch A, Haroske G. Atypical
fibroxanthoma: a series of 25 cases. J Eur Acad Dermatol
- Ang GC, Roenigk RK, Otley CC, et al. More than 2
decades of treating atypical fibroxanthoma at mayo clinic: what
have we learned from 91 patients? Dermatol Surg