A tumor resembles an organ in that it has many specialized cells, i.e., a large number of different genetic signatures and it includes stromal cells, as found in all organs, which provide a foundation and which have a variety of functions. Included in those functions is to provide growth factors and engage in signalling to help cancer cells proliferate and even change in size (grow bigger). However they are suggesting that either local stromal cells must have been differentiated as required or might be recruited by the cancer cells.
A tumor is typically made up of about 40-60% or more of immune system cells. Some are macrophages and neutrophils and many others, which are said to be “alternatively activated”. These are the usual types of immune cells engaged in wound healing and tissue maintenance. These immune cells are one of the major sources of the angiogenesis and stromal growth factors, which are required for wound healing. So the story of cancer cells being “masters of their own destiny” is hardly true. They actively engage with cells of the microenvironment in various forms of signalling and are dependent on the very cells that they are said to be able to evade.. the immune system cells!