Anchoring fibrils in a spindle cell squamous carcinoma.

To the best of our knowledge anchoring fibrils in tumours have been reported to occur only in cutaneous cylindromas and squamous cell carcinomas of oral mucosa and larynx. In this paper we describe a difficult-to-diagnose malignant spindle cell tumour where the striking feature was the presence of large numbers of anchoring plaques and anchoring fibrils in the tumour matrix. On the basis of light microscopic and immunohistochemical studies several diagnoses were preferred, such as malignant fibrous histiocytoma, neurofibrosarcoma, malignant schwannoma, desmoplastic melanoma and spindle cell squamous carcinoma (more fully referred to as 'spindle cell variant of squamous cell carcinoma'). The presence of anchoring fibrils in this tumour strongly supports the diagnosis of spindle cell squamous carcinoma. Our knowledge about the occurrence of anchoring fibrils in tumours is scant, perhaps because they are likely to be missed unless they are present in large numbers, or perhaps because they are mistaken for native collagen fibrils. It seems to us that a systematic search for anchoring fibrils in tumours is warranted, for knowledge about their occurrence or absence in various types of tumours may add yet another diagnostic marker in the armamentarium of the diagnostic electron microscopist and it may also assist in resolving the histogenesis of some controversial neoplasms.