This is the eighteenth blog in a series of blogs on neoplasia.
Though there has been little success in curing the advanced* common cancers, there has been remarkable success in finding cures for some of the rare cancers, particularly several rare cancers of childhood. Why is it possible to cure rare cancers? Why would rarity have anything to do with curability? In this blog, and in the next few blogs, we'll be exploring the properties of common tumors and how they differ from the properties of rare tumors.
As we saw yesterday, the general approach to funding cancer research is the same now as it was in the early 1970s; attack cancer tumor by tumor, dividing available funds in rough proportion to the number of people who die from each tumor.
The only problem with this straightforward approach is that it has not worked very well. Despite decades of funding, We still do not know how to cure the most common advanced (with extensive spread or metastases) cancers occurring in humans.
The reason that we have done so poorly with common tumors relates to the manner in which the common tumors occur.
The human body can be envisioned as a topological donut (Figure below) . Like donuts, we have a continuous surface. We can think of our skin as the outer-edge surface of the donut. We can think of our alimentary tract as the surface of the donut that lines the donut hole. Our outer-edge surface is lined by the epithelial squamous cells of the skin's epidermis. Our inner-edge surface is lined by epithelial enterocytes of the gastrointestinal mucosa.
The donut pastry cells correspond to the non-surface cells of the human body, the cells that arise from human mesoderm, which produces the connective tissues of the body (fibrous tissue, adipose tissue, muscle, bone, vessels). The non-surface cells also include the nervous system and gonads.
Virtually all exposure to toxic and carcinogenic chemicals is via the donut surfaces (the skin, and gastrointestinal tract), and the epithelial organs that bud off these surfaces (lungs, pancreas, liver, breast, prostate). Since the human surfaces contain the cells that are most exposed to carcinogens, it's not surprising that most human cancers are tumors of the surface cells. Just two cancers arising from the outside surface cells (squamous carcinoma of skin and basal cell carcinoma of skin) account for over one million new tumors each year in the U.S., a number that is roughly equal to all the other tumors of the body combined. Tumors of the surfaces account for over 95% of the tumors that occur in humans.
In the next blog, we'll look at the common properties of advanced common cancers that account for their poor cure rate.
-Copyright (C) 2008 Jules J. Berman
*An advanced cancer is one that has directly spread extensively from its primary site or that has metastasized to a distant site
key words: cancer, tumor, tumour, carcinogen, neoplasia, neoplastic development, classification, biomedical informatics, tumor development, precancer, benign tumor, ontology, classification, developmental lineage classification and taxonomy of neoplasms