Nailing down the treatment for ungual melanoma in situ

By Adam Rubin, MD
April 21, 2021
Vol. 3, No. 16

In the recent Dermatologic Surgery manuscript “Nail Unit Melanoma In Situ Treated with Mohs Micrographic Surgery” (1), Dr. Divya Srivastava and her colleagues at the University of Texas Southwestern Medical Center demonstrated the effectiveness of the combination of Mohs micrographic surgery (MMS) and the application of MART-1 staining in the treatment of ungual melanoma in situ (MIS).

The authors present a series of 14 patients diagnosed with nail unit MIS which were treated with MMS employing MART-1 staining over the course of a 10-year period. The entire nail unit was surgically removed, including the proximal nail fold, matrix, nail bed, and hyponychium, with a minimum of 5 mm of tissue from the edge of the clinically evident tumor. MART-1 immunoperoxidase staining was used to define the melanocyte density in the specimens. If positive margins were identified, an additional 3 mm margin was taken and analyzed with the standard MMS technique. Once the patient was cleared of tumor, the excised specimen was sent for permanent section preparation for staging purposes. The average follow-up for the patients was 6 years. Only one patient developed a recurrence (7.1%).

The advantages of MMS over traditional surgical excisions are well known. A distinct advantage of employing MMS for nail unit MIS is the ability to ensure tumor clearance for the patient who then may complete their procedure and treatment in a single visit. Compared to other types of skin specimens, dermatopathology laboratory processing of nail unit specimens, and especially an en bloc excision of the nail unit, will be delayed because of the technical challenges and specialized knowledge needed by the histotechnicians to gross and process the tissue. In order to avoid uncorrectable errors, these specimens are often handled by the most experienced staff so they can be cut and processed correctly the first time, providing optimal results. This delay does not have an effect on the patient if MMS has already been performed and it is known that the patient is free of tumor, and the surgical defect has been repaired. Permanent sections will provide additional information for staging. It is important to note that in this study none of the lesions were upstaged, which, depending on a variety of factors, may result in a change in management.

The importance of the use of MART-1 staining as part of the MMS process cannot be overstated. Identification of melanocytes in the nail unit, even under ideal conditions of use of permanent sections, can be extremely challenging. It is difficult to identify melanocytes on hematoxylin and eosin frozen sections. For accurate diagnoses, use of immunoperoxidase stains in the anatomic area of the nail unit is the norm. David Weedon has written “Although there is little need these days to encourage the further use of immunohistochemistry in the study of nevomelanocytic lesions, there is one group of such lesions in which its use is essential to ensure the correct diagnosis — pigmented lesions of the nail bed/matrix.” (2) For accurate decision making at the time of MMS in and around the nail unit, the value of MART-1 immunoperoxidase staining is incalculable. MART-1/Melan-A staining has been shown to be the preferred marker for melanocytes in the nail unit in general. (3)

While Dr. Srivastava and her colleagues make this look easy, there are significant issues which need to be recognized before a team can start employing this technique. Training and experience of the MMS staff in processing the nail unit tissue is paramount to produce the highest quality sections. Because of the unique anatomy of the nail unit, it is easy to create sections with either false negative or false positive findings. Additionally, for optimal histopathologic analysis, the operating surgeon would benefit from training and experience in leaving the nail plate in place, as opposed to avulsing it.

When at all possible, functional surgery for nail unit melanoma in situ is preferable over amputation to preserve digit functionality. The recurrence rate observed in this study was noninferior to other published studies.

This manuscript represents the latest evolution for the treatment of nail unit melanoma in situ. (4, 5) Over the years increasing evidence has demonstrated the favorability of en bloc excision of the nail unit as the treatment of choice over amputation as therapy. This message needs to be communicated to colleagues in all specialties involved with managing ungual melanomas. Long term follow-up of patients with nail unit melanoma in situ is advised, as recurrences have occurred years after the therapeutic surgical procedure.

Our expert’s viewpoint

Divya Srivastava, MD
Assistant Professor of Dermatology, UT Southwestern Medical Center
Director of Dermatologic Surgery, Parkland Memorial Hospital

The surgical treatment for nail unit melanoma in situ (MIS) has evolved over the last several decades with a trend towards tissue sparing and conservative management. While nail unit melanoma was traditionally treated with distal or proximal amputation, studies show that digit sparing surgery with either en bloc excision or Mohs micrographic surgery (MMS) yields lower recurrence rates. (1) In our practice, we favor MMS to allow for comprehensive margin examination and same day reconstruction, which is optimal for patients. As highlighted by Dr. Rubin, performing MMS is certainly challenging and requires meticulous attention to complex nail anatomy. Exacting training for histotechnicians to competently process the entire nail unit is essential. We believe that this technique enhances patient care. Knackstedt and colleagues demonstrated that digit sparing surgery is associated with minimal change in quality of life and disability compared to a 50-100% impairment in amputation of the thumb. (6) Given optimal recurrence rates and high patient satisfaction with digit sparing surgery, we hope to see further data in the literature supporting the use of MMS for nail unit MIS.

1. Matsumoto A, Strickland N, Nijhawan RI, Srivastava D. Nail Unit Melanoma In Situ Treated With Mohs Micrographic Surgery [published online ahead of print, 2020 Aug 11]. Dermatol Surg. 2020;10.1097/DSS.0000000000002682. doi:10.1097/DSS.0000000000002682

2. Weedon D, Van Deurse M, Rosendahl C. "Occult" melanocytes in nail matrix melanoma. Am J Dermatopathol. 2012;34(8):855. doi:10.1097/DAD.0b013e3182545ccd

3. Wlodek C, Lecerf P, Andre J, Ruben BS, de Berker D. An international survey about nail histology processing techniques. J Cutan Pathol. 2017;44(9):749-756. doi:10.1111/cup.12976

4. Haneke E, Jellinek N. Commentary on Nail Unit Melanoma In Situ Treated With Mohs Micrographic Surgery [published online ahead of print, 2020 Sep 2]. Dermatol Surg. 2020;10.1097/DSS.0000000000002755. doi:10.1097/DSS.0000000000002755

5. Rubin AI. Commentary on Mohs Micrographic Surgery Using MART-1 Immunostaining for Nail Unit Melanoma in Situ [published online ahead of print, 2020 Sep 2]. Dermatol Surg. 2020;10.1097/DSS.0000000000002754. doi:10.1097/DSS.0000000000002754

6. Knackstedt TJ, Baltz JO, Wilmer EN, and Jellinek NJ. Assessing patient outcomes after digit-sparing en bloc surgery of nail apparatus melanoma using two validated surveys. J Am Acad Dermatol. Mar 2020; 82(3): 746-747.