The chapter begins with a list of biological properties that distinguish the rare cancers from the common cancers:
1. Just a few types of common cancers account for the majority of occurrences of cancer.
2. Most of the different types of cancers are rare cancers. Specifically, there are several thousand different types of rare cancers, while there are only a few dozen types of common cancers.
3. Virtually every common cancer is composed of cells derived from the ectodermal or the endodermal layers of the embryo (see Glossary items, Ectoderm, Endoderm). Rare cancers derive from all three germ layers, but the majority of rare cancers derive from the mesoderm.
4. All of the childhood cancers are rare cancers.
5. All the advanced stage cancers that we can currently cure are rare cancers, and most of the curable rare cancers are cancers that occur in children.
6. Inherited syndromes that cause rare cancers are often associated with increased risk for developing common cancers; hence, the causes of rare cancers are related to the causes of common cancers.
7. Rare cancers are genetically simpler than common cancers (i.e., have fewer mutations). In many cases, we know the underlying mutation that leads to the development of rare cancers. We do not know the underlying mutation(s) that leads to common cancers.
8. Common cancers are genetically heterogeneous and may contain one or more rare types of cancer having the same clinical phenotype as the common cancer.
9. Most of what we know about the pathogenesis of cancer has come from observations on rare cancers.
10. The rare cancers serve as sentinels for environmental agents that can cause various types of cancer; either rare or common. Common cancers cannot serve as sentinels.
11. Treatments developed for the rare cancers will almost certainly apply to the common cancers.
- Jules Berman, Ph.D., M.D.