Friday, August 1, 2008

Neoplasms: 20

This is the twentieth 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.

We can cure a few of the rare or uncommon tumors

List. Tumors that can be cured with chemotherapy [1]

- Choriocarcinoma

- Acute lymphocytic leukemia of childhood

- Burkitt lymphoma

- Hodgkin lymphoma

- Acute promyelocytic leukemia

- Large follicular center cell (diffuse histiocytic) lymphoma

- Embryonal carcinoma of testis

- Hairy cell leukemia (probable)

- Seminoma

The new anticancer drugs, targeted at specific pathways activated in tumors, are most effective against rare tumors, characterized by simple, well-characterized mutations and translocations.

A good example is GIST (gastrointestinal stromal tumor). Gist is a rare tumor that is highly responsive to a relatively non-toxic chemotherapeutic agent, imatinib. Many cases of this tumor have a mutation in the C-KIT gene, which codes for a tyrosine kinase receptor that is inhibited by imatinib. GIST is an example of a very simple tumor, that seems to be characterized by a single gene mutation (usually C-KIT), resulting in over-expression of a single protein (tryosine kinase receptor), which is apparently singlehandedly responsible for driving the growth of the tumor, and which can be treated by a non-toxic agent targeted against a specific molecule. Of course, nothing in the field of cancer is ever so simple, and recent studies have uncovered a variety of complicating factors. Still, GIST stands as one of the simplest cancers of humans. Similarly, several other rare tumors characterized by specific tyrosine kinase mutations, including chronic myelogenous leukemia, and systemic mastocytosis, are responsive to imatinib.

It is unlikely that we will develop a cure for the common cancers before we have developed a variety of approaches to curing genetically simple cancers. Sometimes, you need to crawl before you can walk.

1. [Holland Frei Cancer Medicine. Kufe D, Pollock R, Weichselbaum R, Bast R, Gansler T, Holland J, Frei E, eds. BC Decker, Ontario, Canada, 2003.]

-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

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