First, what are metastases? The exact definition of metastases is more and more debated in the last decades (for an excellent review see the review by Welch, 2006), mainly because the advances in cancer research have permitted to unveil new characteristics (genetical, biochemical, surface membrane expression,...) of metastasic cells.
According to Welch, metastases can be defined as
The dissemination of neoplastic cells to discontiguous nearby or
distant secondary (or higher order) sites where they proliferate to
form an extravascular mass of incompletely differentiated cells.
Metastatic process is dependent on three major conditions:
- malignant cells need to adhere to the basement membrane
- local proteolysis (=breakdown of proteins into smaller
polypeptides or amino acids) of the membrane is necessary
- malignant cells need to pass through the rent in the membrane and
the extracellular matrix.
Once these malignant cells are in the circulation, they have to repeat the above mentioned steps at a remote site. Additionally, in order to survive in a foreign tissue, they need to find a "hospitable niche", where they must avoid detection by host defences and warrant blood supply by inducing the growth of new blood vessels.
As you see, the metastatic process is complex and depends on several factors. The rate-limiting step in the metastatic process is the ability for tumor cells to survive and expand in a novel microenvironment. Not all cells have this faculty (so called “metastatic phenotype”) and current evidence suggest that probably only small fraction of tumor cells have this capacity.
Studies have shown that chemokine receptors play a role in the metastatic capacity of a malignant cell. Also, recently, some candidate metastasis-suppressor genes, whose loss of function was associated with metastasis have been identified. Further studies are ongoing in order to understand the genetic and molecular pathways underlying the metastatic process.
So as suggested in one of the comment, the metastic process (and therefore spreading areas) in lung cancer (but also in other type of cancer) is dependent on the malignant cells and on their genotype/phenotype.
Sources:
- Welch DR. Do we need to redefine a cancer metastasis and staging
definitions? Breast disease. 2006;26:3-12.
- Kakinuma T1, Hwang ST. Chemokines, chemokine receptors, and cancer
metastasis J Leukoc Biol April 2006 79:639-651
- Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds.
Harrison's Principles of Internal Medicine, 18e. New York, NY:
McGraw-Hill; 2012.p 681
