The latest installment examines some long extant ideas which while initially dismissed, are now gaining credence. http://www.nytimes.com/2009/12/29/health/research/29cancer.html?pagewanted=1&_r=1&hp
A fundamental concept involves the role that healthy cells surrounding cancerous cells play in either containing cancer or enabling its development. The interplay between healthy cells and adjacent cancerous cells is particularly important and complex as some healthy cells seem to limit the spread of malignant cancers and others seem to become incubators for the spread of malignancy.
The explanation for this is difficult to arrive at but some animal experiments provide some possible insights.
For example, placement of certain tumors in mice into mice embryos are contained by the embryos and do not become cancers as they would in adult mice. In a similar vein, a sarcoma virus which would cause fatal tumors in chickens does not do so when inserted in chicken embryos.
This experiment led to another that may have application to humans. When the sarcoma virus was injected into adult chickens the presumption was that the cancer would develop throughout the bird. Instead, the tumor developed at the injection site where their was a wound but not elsewhere, unless of course there existed a wound elsewhere in which case a tumor developed there as well.
The implication is that wounds or surgeries can potentially enhance cancer development. The full implications of this are little understood but reports of cancer developing at injury sites may be evidence of this phenomenon.