Melanoma: Biopsy Technique And Treatment

James W. Trimble, M.D. and Scott D. Warren, M.D.
James W. Trimble, M.D. and Scott D. Warren, M.D. are Dermatologic Surgeons in private practice.

Introduction

Malignant melanoma can be a lethal skin cancer. Six out of seven skin cancer deaths are from melanoma. Melanoma is more common than any non-skin cancer among women 25-29 years old. The incidence of malignant melanoma doubled among whites between 1973 and 1995. In 1992, in the United States, there were approximately 32,000 new cases and 6,700 deaths resulting from melanoma. In 1999, there will be an estimated 44,200 new cases and 7,300 are expected to die, a 10% increase from 1992. Although there has been an increase in the incidence of melanoma over the past several decades, the five-year survival rate has gradually increased from an overall 41% in 1940, to approximately 83% in the 1990's. Part of this increase in survival has to do with early detection, diagnosis and surgical treatment of primary lesions.

Biopsy

When a suspicious lesion requires diagnosis, the skin biopsy is the single most important test. Information contained in the biopsy will determine management and prognosis of the patient. Selection of the biopsy technique should be done with the awareness of two factors.

First, most melanomas of the skin initially spread within the epidermis. However, all areas of epidermis within the melanoma may not be histologically diagnostic, especially in areas of regression. Therefore, a pathologist may miss classic histologic features needed to make the correct diagnosis. In this regard partial biopsies such as shave or punch excisions, which are less than 5 mm wide, may not include enough horizontal epidermal width to make the correct diagnosis. It is also important to select the darkest, thickest, or most recently darkened area and avoid pale areas of possible regression.

Second, vertical penetration of tumor cells directly impacts prognosis and management. It is critical whenever possible to insure adequate correct tumor penetration measurements. The vertical growth of melanoma is normally reported as tumor thickness measured in millimeters (Breslow tumor thickness) and Clark's level, a histologic reference to the deepest area of penetration into the epidermis, dermis, or fat. Accidental transection of the tumor at a plane above the deepest point of penetration will interfere with the determinations of prognosis and management.

For a lesion which is highly suspicious for melanoma and small enough to be excised, surgical excision is recommended. An elliptical scalpel excision, oriented parallel to the direction of a possible reexcision, should take into account cosmetic or functional factors and should maximize removal of subdermal lymphatics which drain in a proximal direction. A side benefit to elliptical excision occurs with the subsequent stretch of surrounding skin prior to a definitive reexcision. Skin stretching maximizes the ultimate margins which can be excised around a melanoma and can often prevent the need for a skin graft.

For a large pigmented lesion, a lesion of low suspicion, certain anatomic sites (e.g., nose, eyelid, or ear), or by patient choice, tangential excision by shave biopsy is an acceptable alternative. In our experience a flat, nonpalpable melanoma will have a depth of penetration less than 3 mm. In circumstances which preclude excision, a shave biopsy should attempt to reach or exceed this level. Notable exceptions may include congenital lesions, blue nevi, and palpable pigmented lesions with any significant suspicion for melanoma. These lesions should have an excisional biopsy, even if the entire lesion cannot be removed. There is no substantial evidence that biopsy technique (e.g., scalpel excision and tangential excision) affects the mortality or outcome. However, biopsy technique can affect the calculation of the prognosis group. It is critical to provide the pathologist with enough width and depth to make a correct diagnosis and the most accurate measurement of vertical penetration.

Surgical Excision

The treatment of choice of primary melanoma is surgical excision. The margins of excision have ranged up to 5 centimeters decades ago to as little as 1 centimeter in some melanoma subtypes. The appropriateness of margin size in melanoma surgery has changed over time from an aggressive to a more conservative approach, almost in parallel with the change to a more conservative, less radical surgery in breast cancer surgery.

Melanocytes have the capacity to migrate along the dermal epidermal junction 5-10 mm beyond the clinical edge of a tumor. The possibility of in-transit metastasis along superficial or deep lymphatics also exists. It is reassuring that the smaller more conservative surgical margins of today have not resulted in a significant increase in local recurrence.

For melanoma-in-situ (Clark's level 1) surgical excision with a 10-millimeter margin of clinically normal skin is considered adequate. Smaller margins will result in a corresponding increase in local recurrence.

For melanoma 1.0 millimeter or less in thickness (Clark's level II) a minimum of a 1.0 centimeter margin is adequate. The depth of the excision should include full thickness dermis and subcutaneous fat, but not necessarily fascia.

For melanoma of more than 1.0 millimeter in thickness, no universally accepted standard for an excisional margin exists. We would suggest a minimum of 1.5 centimeters in difficult anatomic locations and prefer a 2.0 centimeter margin to include full thickness dermis and fat. In any situation where an elliptical design can encompass a larger margin in the direction of lymphatic flow and not compromise cosmesis or function, the elliptical design is preferred.

Conclusions

There are differing opinions concerning selection of a biopsy technique and surgical margin. We feel that based on various current medical studies the ultimate decision should rest with the physician as he evaluates the lesion, the anatomic site, and the individual patient's concern. We have tried to present a rational approach based on current literature.

BIBLIOGRAPHY

1. Koh HK. Melanoma. Hematology/Oncology Clinics of North America. 1998; 12 (4):681-805.
2. Lang PG. Medical Clinics of North America. 1998; 82(6): 1325-1358.
3. Rigel DS. CA Cancer J Clinic. 1996; 46(4): 195-98.
4. American Academy of Dermatology internet site: http://www. AAD.org

October, 1999/ Jacksonville Medicine

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