Teratomas, neoplasia and differentiation: a biological overview. I. The natural history of teratomas.

In this paper I have attempted to outline the natural history of spontaneously occurring teratomas and associated tumours, but without introducing any preconceptions or assumptions as to their histogenesis or mechanisms of internal differentiation. The justification for this omission is that there is presently no direct evidence in respect of either process in human tumours of this type, with the exception of recent work by LINDER et al. (1975a, b). The various histopathological classifications of teratoid lesions have not been discussed in detail either, because for the most part they have been evolved to serve a specific prognostic purpose on either an empirical basis or on certain histogenetic assumptions. In either case there is an inevitable tendency to emphasize extremes of morphological appearance at the expense of possible continuities of structure and behaviour across the spectrum of teratoid lesions. The purpose of this paper, on the contrary, has been to discern features common to these tumours whenever and wherever they occur. Thus, human teratomas are uniquely puritissular lesions composed, potentially at least, of virtually every recognizable (and probably some as yet unrecognizable), type of embryonic, foetal and adult cell and tissue, together with, in some cases, frankly malignant cells of no obvious derivation or differentiation. In spite of the occasional appearance of structures resembling pre-somite embryos (embryoid bodies), there is no compelling evidence that human teratomatous histogenesis recapitulates embryogenesis in any strict fashion. Histologically, the overwhelming impression is of a more or less random association of cells and tissues at different stages of development and differentiation that proceed up to but not beyond organogenesis. Such teratomas are found at a number of well-defined sites, of which the sacrococcyx is the most prominent in infancy and the gonads during adult life. Both gonadal and extragonadal sites are also associated with apparently homogeneous neoplasms containing cells with features reminiscent of early stages of germinal differentiation which evoke, in many cases, a marked stromal and lymphocytic response, the so-called germinomas. In 'mixed' tumours, which are recognized in an increasing proportion of cases, there is karyological evidence of a conjoint rather than separate origin of teratomatous and germinomatous elements in at least some tumours, challenging a long held belief in their invariably separate character (e.g. HALLEY, 1963).