- Who can get cancer?
- Consider the source
- Consider the science
- Types of human studies on cancer risk
- Studies that observe humans
- Human testing: Clinical trials
- A closer look at the evidence
- Other questions about studies on new ways to prevent cancer
- What does this mean to you?
- To learn more
- Appendix A
Consider the science
If you want to use proven methods to prevent cancer, look at how the method was tested. The way tests are set up can affect the outcome, and sometimes can make it seem that a method or substance prevents cancer when it really doesn’t.
Lab and animal studies: Pre-clinical tests
Scientists usually start by testing a new prevention method or treatment on cells in a dish in the lab, to find out if it has any effect there. They may treat cells with a known cancer-causing agent, for instance, and then add the new compound to see if it stops pre-cancerous changes in the cells. If it doesn’t, they may change the formula or use different types of cells to try it again. Sometimes studies like this that show some effect on the cells are published. News broadcasters may treat the study as proof that a cancer prevention method works. But just because a compound stops abnormal cell growth when it’s added to cells in a lab dish does not mean that it will work in the human body.
This means that if you are looking at a report of a research study – even one that says a treatment “stops cancer cells” – you may notice that there’s no mention of people. Some of these lab studies use human cancer cells, but others use cancer cells from animals. (Either way, studies done on cells alone are called in vitro studies.)
At this point, anything that stops cancer cells may sound like good news. But there are many compounds that can keep cancer cells from growing in a lab dish that do not work when people take them.
Some reasons a treatment may not work for people is that the substance also hurts or kills normal cells, or because the body cannot absorb it and get it to the place where it’s needed to stop cancer. Sometimes, even if the substance can be absorbed, can reach all the body tissues, and doesn’t harm normal cells, the amount of the substance that gets to the tissues isn’t enough to stop the cancer cells. There are many hurdles between lab studies and human ones.
If the researchers find the effect they want in cells in a dish, they may move on to animal tests. This can help them find out if the substance can be absorbed from the stomach or intestine, and learn how it’s distributed in the animal’s body. They may look for good and bad effects. Because some of these study reports are published, you may also hear about them on the news. These are called in vivo studies. This means that they were studied in living creatures.
If the study was done in animals, good outcomes may sound promising. But methods that work in animals don’t always work when they are tested on people. Animal studies often help scientists know which drugs may be toxic (dangerous or poisonous) to people, and which may show unexpected effects. Sometimes a drug or food supplement turns out to do almost the exact same things in people as animals. But as any veterinarian can tell you, there are many drugs people use that don’t work on animals, and vice versa. Some foods and drugs that are safe for animals can hurt people, and some foods and drugs that are safe for humans can hurt animals. So while animal tests can give researchers certain types of valuable information, they still may not show how the compound will affect people.
News stories on lab and animal studies can mislead
In both lab studies and animal studies, the research report may be published. Usually, the researcher’s own report will make it clear that more studies need to be done to see if the substance makes a difference in people. But if a news group picks up the story and publishes it, they may not mention how the study was done.
Often the headlines, and sometimes even the full story, do not clearly say what kind of study is being reported. Sometimes the news reports on this very early research may make it sound like the compound will work in people, which can lead to confusion. This is why it helps to look at the whole printed story, and then see if you can find out more about the details of the research. Always keep in mind that there’s a huge difference between positive results in lab or animal studies and good results in human studies.
Last Medical Review: 09/04/2012
Last Revised: 09/04/2012