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Introduction to Symposium V

In truth, the entire program of this joint United States Japan Histochemical meeting reflects the contribution of "Histochemistry to Medicine." However, this Symposium is central to the interests of those of us who are pathologists. The first three papers this morning deal with specific aspects of oncodevelopmental medicine and the remaining papers concern a number of widely used techniques in clinical pathology that are relevant to clinical laboratory practice. Oncodevelopmental biology deals with the interface between embryology and oncology. Thus, the reexpression of oncofetal proteins or the persistent expression of embryonic genes are facets of oncodevelopmental biology and medicine. That such expression may endow cells with properties shared between embryonic and cancer cells could provide a plausible epigenetic explanation of neoplasia. In this context we would regard "cellular oncogenes" more precisely as "oncodevelopmental genes." In presenting an embryologic classification of tumors (1) an early event in their development has recently assumed prominence. It is the various specialized migratory embryonic cells and their progeny, e.g., neural crest cells, germ cells, Ccells, hematopoietic cells, etc. Their eutopically expressed polypeptide hormones have provided diagnostic markers for a whole newly recognized category of their embryonic tumor counterparts. The expression of oncotrophoblast genes in cancer cells is an example of the neoplastic counterpart to the extraembryonic structure recognizable as early as the seventh day of gestation. There are developmental phase-specific genes for early and term placental alkaline phosphatase (2) that are reexpressed in cancer cells. A key question being pursued in my laboratory relates to whether or not the gene product is identical in tumor cells to the placental isoenzyme. Of value in this regard are a number of monoclonal antibodies that are being employed to map out the several domains of the enzyme molecule. Enzyme immunocytochemistry has been playing a vital role in visualizing the trophoblast gene products in cancer cells. Finally, in examining the various concepts of the etiology of cancer, it is clear that up to 1968 these were fashioned to the biochemical fads of the day, ranging from Warburg manometry to enzyme patterns in growing tumors. From 1968 on, more and more stress was placed on biological concepts with terms such as "blocked ontogeny," "dysdifferentiation," and "retrodifferentiation." These can all be accommodated in the area of oncodevelopmental gene expression. From these perspectives on cancer etiology we can hope to understand the niche of each of the presentations that follow.