Roberto N. Gonzales jr.

PBLI on MALIGANANT MELANOMA

 

Clinical Management: Choice of Biopsy

 

A comprehensive treatment plan for melanoma is dependent on accurate diagnosis and complete assessment of the histologic features that compose the prognostic indicators. Careful examination of the skin is a critical first step in diagnosis. Any lesion that has irregular borders, variations in pigmentation, black color, or an irregular surface (especially if it has undergone a recent change); is raised; or has begun to itch or to bleed should arouse suspicion. To make a diagnosis, a full-thickness biopsy should be performed. If the lesion is small, an excisional biopsy into subcutaneous fat should be performed. The lymph node basins draining the region of the lesion also must be examined carefully.

It has been shown that the clinical diagnosis of melanoma is accurate in only approximately 65% of cases. It is not uncommon for patients who present with melanoma to give a history of a prior lesion at the same site, treated in the past by cautery or cryoablation, without histologic evaluation. When such a patient presents to the melanoma clinic with metastatic disease, the preceding sequence of events has been particularly tragic.

The principles that are advised for biopsy of lesions suspected to be melanoma are

(1) always take full-thickness biopsy samples

(2) include a rim of normal skin in the biopsy sample

(3) on extremities, orient the incision longitudinally.

 A full-thickness biopsy should, by definition, include all layers of the skin, so the subcutis is entered during the biopsy. This is usually done by excising a small ellipse of skin with a scalpel. Normal skin included in the biopsy need not be extensive. A 1- to 2-mm margin of normal skin will permit the pathologist to examine the junctional changes that are critical to identifying melanoma and to determining whether it is a primary or a metastatic lesion. These biopsies are easily performed in the outpatient/ambulatory setting. No preoperative laboratory studies have to be performed. Under local anesthesia, the lesion is then excised with a 1- to 2-mm margin, lifting the skin up with an Adson forceps. Hemostasis can usually be achieved without electrocautery through a combination of gentle pressure and suture closure. The incision is closed, in many cases, with a subcuticular 4-0 absorbable suture and Steristrips. If there is significant tension, a few interrupted nonabsorbable 4-0 sutures will suffice. The wound can be covered with a sterile dry dressing for 2 to 3 days.

Although complete excisional biopsy is ideal, there may be some cases (i.e., of large facial lesions) when complete excision of a pigmented lesion would be unreasonably deforming. In those cases, excision of the portion of the lesion of greatest concern may be adequate for a diagnosis. Again, some normal skin should be included at a margin. It is important that the full thickness of the lesion be evaluable in the biopsy. Because wide reexcision is always performed after the biopsy, partial excision of a melanoma is not generally thought to compromise subsequent therapy. The outcome is the same for punch, incisional, excisional, or wide excisional biopsies. [36] However, the possibility of effects on prognosis has not been ruled out. [3] Thus, it is wise to perform complete excisional biopsy when feasible.

In some cases, a punch biopsy technique may be useful, such as with small nevi. A punch biopsy instrument is a disposable circular blade on a handle that can be used to excise a small circle of full-thickness skin. Punch biopsy instruments for excisions 4, 5, or 6 mm in diameter are useful for quick excisions of small nevi, but it is important when using them to be certain the lesion can be completely excised with a 1- to 2-mm margin and to be careful not to crush the lesion when excising it. After punching out the skin, the circle of skin containing the lesion must be excised with scissors just below the dermis. A fine forceps can be used to elevate the skin circle while cutting underneath it. After excision, the lesion should be placed in formalin and sent for histologic evaluation. Lesions larger than 2 to 4 mm should not be excised with a punch biopsy because the evaluation of the junctional zone, at the edge of the lesion. can be very important for a definitive diagnosis.

At least as important as these instructions is the choice of skin incision. Especially on extremities, the orientation of the initial skin biopsy is a critical determinant of the subsequent therapy. If the pigmented lesion is melanoma, a wide excision will be needed, the orientation of which is determined largely by the orientation of the initial excision. It is difficult to close a transverse incision on an extremity primarily; thus, a transverse incision is more likely to require a skin graft. Also, because the innervation to skin surfaces runs longitudinally, a transversely oriented excision will interrupt more of the innervation to skin distal to the lesion. On the other hand, if an incision crosses a joint, it may lead to a contracture that limits range of motion, so extremity excisions near a joint may need to be oriented transversely or may need to be closed with a Z-plasty across the joint. On the head and neck region, the orientation of a biopsy incision should be selected with consideration of how it may affect subsequent reexcision or node dissection incisions.