The biology of the cell is very, very complex. New important mechanisms and systems of regulation are still being discovered, and many of those already known remain incompletely understood. But every newly discovered system offers the possibility of ways to reign in cancer. Given that cancerous cells are normal cells run wild and mutant, overtaken by errant molecular machinery, we'd like to think that there are simple ways to bring it all crashing down - a single molecule that will be a spanner thrust into the works of cancer.
Some research hints that if you dive deeply enough into cellular mechanisms, you'll find something useful. An example that recently cropped up is the use of microRNAs, vital components in processes that dynamically regulate gene expression, first discovered in the early 1990s. You might want to start with the press release:
Noticing the conspicuous absence of single-stranded genetic snippets called microRNAs in cancer cells, a team of researchers from Johns Hopkins and Nationwide Children's Hospital delivered these tiny regulators of genes to mice with liver cancer and found that tumor cells rapidly died while healthy cells remained unaffected. Researchers have shown that replacement of a single microRNA in mice with an extremely aggressive form of liver cancer can be enough to halt their disease.
This is what I'd call solid engineering work. They don't know why this works, but proceeded to test on the basis of an observation and obtained a good result. Onward and upward: firstly you don't always need to know all the details of how things work in order to achieve great things, and secondly the march of biotechnology is making such speculative testing ever cheaper and thus ever more feasible. Restoring the microRNA most likely enables one of the many suicide switches present in our cells, a switch disabled by the specific mutations that led to that form of cancer.
Looking at the paper:
Systemic administration of this miRNA in a mouse model [results] in inhibition of cancer cell proliferation, induction of tumor-specific apoptosis, and dramatic protection from disease progression without toxicity.
A viral vector was used to deliver the microRNA (or miRNA), but I wanted to draw attention to the fact that the microRNA was not targeted to specific cells; it's an example of a therapy introduced to every cell but that only harms cancerous cells. Ergo no side-effects, something we also see in many targeted therapies presently under development in the laboratory. Patients won't suffer due to their treatments under the next generation of cancer therapies, a great improvement over most present drugs and chemotherapies.
Kota, J., Chivukula, R., O'Donnell, K., Wentzel, E., Montgomery, C., Hwang, H., Chang, T., Vivekanandan, P., Torbenson, M., & Clark, K. (2009). Therapeutic microRNA Delivery Suppresses Tumorigenesis in a Murine Liver Cancer Model Cell, 137 (6), 1005-1017 DOI: 10.1016/j.cell.2009.04.021