Pitfalls and important issues in the pathologic diagnosis of melanocytic tumors

Abstract

In Australia and many other countries, melanoma is a major public health problem, particularly in those individuals of Celtic ancestry. Other races are not immune, especially when acral and mucosal sites are taken into account. Accurate diagnosis requires the balancing of clinical data (including patient age and sex, family history, the anatomic site of the lesion, the history of the lesion, and other factors such as a history of trauma, sunburn, or pregnancy), histologic features (including architecture, cytology, and the host response), awareness of pitfalls, and judgment. Several types of nevi-such as regenerating nevi, combined nevi, acral nevi, deep penetrating nevi, and Spitz nevi-are prone to be misdiagnosed as melanoma. Melanomas often underdiagnosed include the nevoid, desmoplastic, Spitzoid, and regressed types. The type of biopsy and suboptimal processing may also significantly influence the diagnosis.

Keywords: Biopsy; clinical; diagnosis; melanoma; misdiagnosis; morphology; nevus; pathology; pitfalls.

Figure 1

Dysplastic compound nevus. Note lentiginous and nested melanocytic proliferation and periretal lamellar collagen.

Figure 2

A and B, Combined nevus with dermal nevus and deep penetrating nevus components. C, Many of the deep penetrating nevus cells are lightly pigmented and positive for HMB45.

Figure 3

Conventional (dendritic) blue nevus.

Figure 4

Deep penetrating nevus. A, Note “V”-shaped architecture. B and C, The cells shows moderate nuclear variation and occasional intranuclear pseudoinclusions.

Figure 5

A–D, Regressing (“halo”) intradermal Spitz nevus. B and C, The plump epithelioid melanocytes have eosinophilic glassy cytoplasm and are dispersed among an infiltrate of small lymphocytes. D, The melanocytes show strong positivity (nuclear and cytoplasmic) for S-100 protein in contrast to the interspersed small lymphocytes.

Figure 6

Nevoid melanoma. Note the thin, elongated rete ridges of the epidermis (A) associated with expanded dermal papillae containing nevoid melanocytes of intermediate size (B). On high power (C), the cells show nucleoli and occasional mitoses.

Figure 7

Desmoplastic neurotropic melanoma. A, A subtle spindle cell proliferation is present, extending to the inked surgical margin. Note the associated clusters of lymphocytes, which often represent an important clue to diagnosis. B, Some nuclei are elongated and hyperchromatic. C, The neurotropism in this case is predominantly intraneural.