Well, the previous statement is not that kind of "black and white" one - I would say that cancer cells, at least in vitro, are, when it comes to contact inhibition due to increased density, less density-dependent than normal cells, yes! But, still you can see that many of them markedly slows down their growth in high density cultures, leading to increased accumulation of cells in the G0/G1-cell cycle phase and less amount of cycling cells (diminished S-phase). However, there is great variation depending on which cell line you study, some are more, others less contact inhibited. On the other hand, increased contact between cancer cells in in vitro cultures often increase their resistance to cell death/apoptosis, maybe (at least partly) secondarily to the G0/G1-accumulation and/or decreased S-phase. This is one of the reasons why 3-D cultures has gained a lot of interest during the recent years. In these, tumor cells are grown in immediate proximity to each other, in clumps/aggregates actually, and sometimes with other (normal) cell types as well, just like the situation in the tumor in situ/in the body. These cells shows much lower proliferative activity, and often completely different responses to drugs as compared with traditional 2-D cultures.

So, to conclude, most likely your cells, at least when it comes to gene expression related to cell cycle, would show obvious differences if you compare e.g. cell cultures harvested at low density with cell cultures harvested at high density (100% confluency).

Cancer cells do not exhibit density dependence, hallmark of cancerous cells, so the gene expression may be limited due to density in cell culture. Additionally, it would depend on the type of cancer.

TNF A gene expression in liver cancer cells has been shown to be influenced by density in culture. Attached is the article for reference.

http://www.spandidos-publications.com/ijo/31/6/1485

Well, the previous statement is not that kind of "black and white" one - I would say that cancer cells, at least in vitro, are, when it comes to contact inhibition due to increased density, less density-dependent than normal cells, yes! But, still you can see that many of them markedly slows down their growth in high density cultures, leading to increased accumulation of cells in the G0/G1-cell cycle phase and less amount of cycling cells (diminished S-phase). However, there is great variation depending on which cell line you study, some are more, others less contact inhibited. On the other hand, increased contact between cancer cells in in vitro cultures often increase their resistance to cell death/apoptosis, maybe (at least partly) secondarily to the G0/G1-accumulation and/or decreased S-phase. This is one of the reasons why 3-D cultures has gained a lot of interest during the recent years. In these, tumor cells are grown in immediate proximity to each other, in clumps/aggregates actually, and sometimes with other (normal) cell types as well, just like the situation in the tumor in situ/in the body. These cells shows much lower proliferative activity, and often completely different responses to drugs as compared with traditional 2-D cultures.

So, to conclude, most likely your cells, at least when it comes to gene expression related to cell cycle, would show obvious differences if you compare e.g. cell cultures harvested at low density with cell cultures harvested at high density (100% confluency).

If we want to compare results, a density of cells exposed to different cytotoxic agents should be the same.

We published a study looking at human fibroblasts some years ago. While this study dealt primarily with DNA damage it includes studies of profiles that depend on how the cell cycle.

Zhou, T., Chou, J. W., Simpson, D. A., Zhou, Y., Mullen, T. E., Medeiros, M., Bushel, P. R., Paules, R. S., Yang, X., Hurban, P., Lobenhofer, E. K., Kaufmann, W. K., 2006. Profiles of global gene expression in ionizing-radiation-damaged human diploid fibroblasts reveal synchronization behind the G1 checkpoint in a G0-like state of quiescence. Environ Health Perspect 114, 553-9.

The experiment and observation done on non-cancerous cell lines can not be extrapulated for the human cancer cell line as the properties you mentioned is true for normal cell lines but not for cancer cell line lines e.g. as contact inhibition is not followed by the cancer cell lines etc.