Mohs micrographic surgery increasingly used for melanoma.25-31 This procedure may be performed with frozen or permanent sections, using concomitant immunohistochemical staining with either method of embedding. This has been especially useful in cosmetically sensitive areas such as the face, ear, nose, genitalia, and extremities.30 Mohs micrographic surgery with permanent sections also makes possible the most definitive surgical margin analysis.
TABLE 2
Recommended incision margins
| BRESLOW THICKNESS | EXCISION MARGINS (CM) |
|---|---|
| In situ | 0.5 |
| <1 mm | 1 |
| 1–4 mm | 1–2 |
| >4 mm | 2–3 |
Sentinel lymph node biopsy
Lymphatic mapping and sentinel lymph node biopsy have significantly changed the initial approach to the patient with melanoma and have reinvigorated debate over the importance and management of regional lymph nodes in cutaneous malignant melanoma. The anatomic basis of, and techniques for, lymphatic mapping and sentinel lymph node biopsy are well-described elsewhere and are not reviewed here.32
Risk factors
Risk factors for melanoma include a personal or family history of melanoma and the presence of multiple nevi. Nevi are considered risk factors if an individual has many or if the nevi are unusual in appearance or size. Other risk factors include fair complexion, excessive sun exposure, history of severe sunburns, use of tanning booths, immunosuppression and occupational exposure to certain chemicals.1
Ultraviolet light exposure remains the most well-described risk factor for the development of cutaneous melanoma; however, the pathogenesis remains largely unknown.3,4 This is especially true in patients with increased ultraviolet sensitivity secondary to fair skin type and a tendency to burn. The use of sunscreen is recommended for prevention of all types of skin cancer; however, its use may promote increased ultraviolet exposure from a false sense of protection.5,6 Additionally, proper application (i.e. frequent reapplication) is seldom performed.
Histolopathologic data from regional lymph nodes is the most important prognostic factor for cutaneous melanoma,13 and sentinel lymph node biopsy is proven as a staging procedure—as reflected in the revised AJCC TNM Staging System published in 2001 (TABLES 1 AND 2).13 This staging system differs from the previous one in several ways:
- Thickness and ulceration are the primary predictors of survival with localized melanoma (stages I and II)
- Number of metastatic lymph nodes involved and tumor burden are most important predictors of survival in stage III melanoma
- Anatomic site of metastasis (distant) and presence/absence of elevated lactate dehydrogenase (LDH) are primary predictors of survival with stage IV melanoma
- Ulceration should prompt an overall upstaging for melanoma stages I–III
- Satellite metastases around a primary melanoma and in-transit metastases together indicate a stage III melanoma
- Staging decisions are based on sentinel node biopsy/lymphatic mapping.13
Multiple studies have reviewed the changes between the new and old TNM staging systems for melanoma.13
When to biopsy. Clinical experience supports reserving lymphatic mapping and sentinel lymph node mapping for patients with primary lesions 1 mm or thicker. Some authorities have recommended sentinel lymph node biopsy for lesions <1 mm thick if they are ulcerated or if a discrepancy exists between the Breslow tumor thickness and Clark’s level. For such lesions, biopsy has been recommended for Clark’s level >III.33
Though sentinel lymph node biopsy can be performed successfully after wide local excision, doing it before excision will prevent disruption of lymphatics for node mapping.34 The sentinel lymph node should be submitted to pathology for permanent section analysis. Frozen section analysis is not recommended for melanoma due to its lower sensitivity.35
Though not widely adopted, some surgeons use intraoperative touch prep cytology as part of an initial intraoperative evaluation.36 If the surgeon is prepared to proceed with regional node dissection and a “black” grossly involved node is encountered, intraoperative frozen section may be used to confirm metastastic melanoma. Neither touch preps nor frozen sections are likely to demonstrate the small, isolated metastatic tumor cells commonly identified in small, grossly normal lymph nodes.
What to expect from the pathologist. If blue dye is used for localization, the pathologist should document the presence of that color in the lymph nodes submitted. Outside of a clinical trial, fresh lymph node tissue is not usually preserved for polymerase chain reaction (PCR) or other molecular methods for detecting tumor cells.
Although examination techniques vary in some details among institutions, general principles are well accepted and include submission of the entire lymph node, step or serial sections, and, when initial sections do not reveal metastatic tumor, use of immunohistochemistry for melanocyte-associated antigens (see Immunohistochemical techniques and antibody testing).
Fine points regarding interpretation of sentinel lymph nodes. First, the rationale behind biopsy of sentinel lymph nodes is that the lymphatic system is a potential means of metastasis. However, it is not the only means of spread. Hematogenous and tissue spread are potential mechanisms as well.