Evaluation of spindle cell tumors.

The most important aspect of any evaluation of spindle cell tumors in the skin or superficial soft tissues is the clinical examination, as a great deal can be learned from the location, appearance, and size of the tumor in question. As recounted in this chapter, the histologic features of these tumors may also be distinctive; however, in some instances, histologic examination alone is insufficient for diagnosis. In such cases, electron microscopy holds considerable promise, but the technique is too dependent upon both the availability of adequately preserved tissues and access to the technique itself. As a result, immunohistochemistry remains the favored approach to most problematic lesions. In our experience, at least 90% of histologically enigmatic tumors will exhibit a characteristic immunophenotype, the remainder usually being indeterminant for a specific pattern of differentiation. The latter outcome is often the result of improper tissue preservation, but may also reflect the primitive nature of some neoplasms. Fortunately, the least common outcome is an ambiguous or "mixed-lineage" phenotype, in which neither one of two or more patterns of differentiation is resolved with certainty. The most common settings in which these problems arise are the separation of MPNST from LMS, and the recognition of melanocytic lesions as distinct from tumors of peripheral nerve sheath. The latter is clearly of greatest clinical concern, and should be the focus of additional study.