As promised, a more in depth look at the role of genetics in cancer:
Cancer is, by definition, mutant cells. Somewhere in the cell line, a cell had an abnormality in it's propagation control and it's DNA damage control checkpoints. This allows the cell to propagate without check no matter what damage it accrues.
This abnormality happens in two main ways: oncogenes, which cause cell growth and multiplication, and tumor suppressor genes, which prevent excessive cell growth. Cancers occur when either oncogenes are amplified or tumor suppressors are suppressed. Usually, these mutations happen in cell line, and then cause a tumor to develop in that specific site. One example of this is mutations caused by tobacco in lung cells, which causes a lung carcinoma. Sometimes, these mutations occur when the embryo forms, known as germ line mutations. These are commonly associated with high incidences of childhood cancer, such as Li-Fraumeni syndrome.
Lots of research has been done in the past few years about the role genes play in cancer, especially in childhood cancers. Because there hasn't been enough time for carcinogens to build up to the level of causing a tumor, most childhood cancers are thought to caused by genetic abnormalities.
Researching the genetics of cancer cells also provides the ability to target treatments to the specific mutations they have. An example of a targeted treatment is Gleevec for the treatment of Philadelphia Chromosome CML. With increasing research, it is hoped that many cure rates will be greatly improved with genetically targeted treatments.