- This document only addresses ways to look at information on methods that are said to prevent cancer, but some of the same principles can be used when looking at information on cancer treatment, sympto
- Look at the science behind the prevention method
- 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
Look at the science behind the prevention method
To find a cancer prevention method with a proven track record, look at how the method was tested. The way tests are set up can affect the outcome, and sometimes can make it look like a method or substance prevents cancer when it really doesn’t.
Studies in cells (laboratory studies)
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 and then add the compound they’re testing 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 show some effect on the cells, and they’re published. News broadcasters may then 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're looking at a report of a research study – even one that says a treatment “stops the growth of 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 don’t work or aren’t safe in people.
Some reasons a treatment might not work for people is that the substance also hurts or kills normal cells, or because the body can’t 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.
Studies in animals
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 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 to people, and which may have unexpected effects. Sometimes a drug or food supplement turns out to do almost the exact same things in people as animals, but many don’t work for one or the other. And as any veterinarian can tell you, some foods and drugs that are safe for animals can hurt people, and some foods and drugs that are safe for people 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 makes 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 or that more study is needed.
Often the headlines, and sometimes even the full story, do not clearly say what kind of study was done. Sometimes the news reports on this very early research may make it sound like the method 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: 10/09/2014
Last Revised: 11/21/2014