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Biopsies of pigmented lesions often aim for complete removal, but in many clinical situations, a lesion is partially sampled. When a biopsy has a positive deep or lateral margin, clinical information is incomplete and may not be able to be reconstructed after subsequent procedures. In addition to confounding clinical information for prognosis and treatment, there is a theoretical risk of adverse clinical outcomes caused by melanoma transection. Fortunately, new evidence confirms that incisional biopsy of melanoma, while not ideal, is not associated with worsened clinical outcomes.

When suspicion is high for melanoma, excisional biopsy is almost always the diagnostic test of choice. Biopsies of pigmented lesions often aim for complete removal, but in many clinical situations, a lesion is partially sampled. The partial sampling may be deliberate, as with a large or cosmetically sensitive lesion, or may be found incidentally on histopathologic examination. Some pigmented lesions are transected at the deep margin, and others at a lateral margin. When the lesion in question is a melanoma, these partial sampling challenges can lead to errors in correct diagnosis (most importantly, tumor depth) and potentially can complicate therapy and outcomes.

Hypothetically, incisional biopsy could spread tumor cells locally or via blood or lymph vessels, or could trigger a wound healing response that could also promote tumor cell growth. Initial data suggested that incisional biopsy could lead to poorer clinical outcomes. However, incisional biopsy is often obtained on large melanomas or those in difficult-to-treat areas such as the head and neck and may lead to a selection bias for incisional biopsy for tumors with poorer outcomes.

Partial sampling errors have a role in medical malpractice, and at least 30% of pathology cases among a set of claims in California were due to missed melanoma diagnoses. In a large US physician insurer, The Doctors Company, more than 50% of the false-negative missed melanoma diagnosis cases were due to partial sampling.¹

New, larger studies reviewed here have addressed the incidence of partial biopsy for melanoma and its effect on outcomes. Fortunately, these data confirm that while not ideal, partial sampling or transection of melanoma does not significantly affect long-term outcomes. These studies retrospectively analyze confirmed melanoma cases rather than detecting potentially missed diagnoses.

The largest case-control series analyzed the Scottish Melanoma Group's tumor registry from 1979 to 1995 to evaluate whether incisional biopsy of melanoma might affect prognosis compared with excisional biopsy.² This group of cases included only invasive melanoma that was diagnosed by incisional biopsy, and each was compared with 2 controls that had only excisional biopsy. Groups were matched by Breslow thickness as thin (<1.5 mm), intermediate (1.5 to 3 mm), or thick (>3 mm) melanoma. Clinical outcomes were time to melanoma recurrence and melanoma-specific mortality. Among more than 5,700 melanoma patients, only 321 had incisional biopsy before definitive excision. Two hundred seventy invasive melanomas diagnosed by incisional biopsy were matched to 496 controls based on age, gender, tumor depth, and tumor location. The main outcome measures were time from initial biopsy to tumor recurrence and to melanoma-related death.

Their analysis showed that biopsy type had no significant effect on recurrence (P=.30) or melanoma-related death (P=.34). This population is notable in being limited to individuals with invasive melanomas and having a larger proportion, approximately 36%, of deep melanoma cases. Subungual, mucosal, and palm and sole melanomas were underrepresented because appropriately matched controls were not always available in the group.

In 2010, an Australian tertiary referral center compared partial and excisional biopsy techniques in a series of more than 2,400 consecutive cases of melanoma referred between 1995 and 2006.³ In Australia, excisional biopsy was overwhelmingly the preferred diagnostic technique. At least 2,000 of the 2,400 cases were evaluated with excisional biopsy, and fewer than 200 each were diagnosed with shave or punch biopsy. Odds ratios were compared for rates of correct diagnosis.

Researchers compared excisional biopsy, shave biopsy, and punch biopsy on rates of misdiagnosis. Other factors considered were anatomic site, physician type at initial management, hypomelanosis, melanoma subtype, biopsy sample size, multiple biopsies, and tumor thickness. Missed diagnoses were examined for both falsepositive and false-negative results, and false-negative results were further classified as to whether they led to an adverse outcome. For the purposes of this study, an adverse outcome was defined as the persistence or progression of primary disease or development of nodal or distant metastasis occurring before the correct diagnosis. False-negative cases were usually detected on definitive excision, though cases were at times diagnosed as dysplastic nevi or nonmelanoma skin cancer and reclassified on reexcision, or were repeatedly sampled because of lesion persistence or clinical progression. Most false-positive lesions were reclassified after excision as benign nevi, dysplastic nevi, or Spitz nevi.