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Research Updates

When is Mohs Micrographic Surgery Appropriate?

Lee Miller, Daniel Pearce

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 extirpation.

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).

 

 

Common Tumors

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.
 

 

Tissue Sparing

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 advantages.

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.7

Rare Tumors

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

Conclusions

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 surgery.
 

References

  1. 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.
  2. Cook J, Zitelli JA. Mohs micrographic surgery: a cost analysis. J Am Acad Dermatol 1998;39:698-703.
  3. Wolf DJ, Zitelli JA. Surgical margins for basal cell carcinoma. Arch Dermatol 1987;123:340-344.
  4. 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 1989;15:315-328.
  5. Minton TJ. Contemporary Mohs surgery applications. Curr Opin Otolaryngol Head Neck Surg 2008;16:376-380.
  6. Tefler NR, Colver GB, Bowers PW. Guidelines for the management of basal cell carcinoma. Br J Dermatol 2008;159:35-48.
  7. Perkins W. Who should have Mohs micrographic surgery? Curr Opin OtolaryngolHead Neck Surg 2010;18:283-289.
  8. 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 2005;53:464-468.
  9. Lemm D, Mugge LO, Mentzel T, Hoffken K. Current treatment options in dermatofibrosarcoma protuberans. J Cancer Res Clin Oncol 2009;135:653-665.
  10. Paradisi A, Abeni D, Rusciani A, et al. Dermatofibrosarcoma protuberans: wide local excision vs. Mohs micrographic surgery. Cancer Treatment Rev 2008;34:728-736.
  11. Wollina U, Schonlebe J, Koch A, Haroske G. Atypical fibroxanthoma: a series of 25 cases. J Eur Acad Dermatol Venereo 2010;24:943-946.
  12. 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 2009;35:765-772.
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