<b>Phase I studies</b><br>The purpose of a phase I study is to find the best way to give a new treatment and how much of it can be given safely. In a phase I study, a new treatment is given to a small number of patients. For a new drug, the study starts by giving a very low dose of the drug, then the dose is slowly increased as new patients enter the trial. The dose can be increased by giving more at one time or by giving the same dose more often. Physicians watch patients carefully for any harmful side effects. Although the research treatment has been well tested in laboratory and animal studies, the side effects in patients can not be completely known ahead of time. Phase I studies may involve significant risks for this reason. They are offered only to patients whose cancer cannot be helped by other known treatments. Phase I treatments may or may not produce anti-cancer effects, but some patients have been helped by these treatments. Once the best dose is chosen, the drug is studied for its ability to shrink tumors in phase II trials. 

<b>Phase II studies</b><br>are designed to find out if the treatment actually kills cancer cells in people. Usually groups of 20 to 50 patients with one type of cancer receive a phase II treatment. For example, patients with breast cancer that no longer responds to accepted therapy (it has become resistant to standard therapy) may be treated on a phase II study. Patients are closely observed for anticancer effect by repeated measurement of tumor size to see if it has shrunk since the beginning of the study. When the tumor gets a lot smaller and stays smaller for at least a month, the patient is said to have "responded" to the treatment. If at least one-fifth of the patients in the phase II study respond to treatment, the treatment is judged active against their tumor type. In addition to monitoring patients for response, any side effects of the treatment are carefully recorded and assessed. Since larger numbers of patients receive the treatment in phase II studies than in phase I studies, there is more chance to observe unusual side effects. Each new phase of a clinical trial depends on and builds on information from an earlier phase. If a treatment has shown activity against cancer in a phase II study, it becomes part of a phase III study. 

<b>Phase III studies</b><br>usually compare standard treatments (the treatment most accepted) with treatments that appeared to be good in the small phase II studies. Phase III studies require large numbers of patients; some studies use thousands of patients. Patients are usually randomized, which means they are assigned by chance to one of the treatments being studied. The group that receives the standard treatment is called the "control" group. The researchers know that a certain number of these patients will be helped by the treatment. Another patient group receives the newer therapy to see if it will help the patients more. Phase III studies look for longer life, better quality of life, fewer side effects, and fewer cases of the cancer returning. 

<b>Adjuvant studies</b><br>Adjuvant studies are conducted to determine if additional therapy will improve the chance for cure in patients at risk for the cancer coming back after surgical removal of all visible disease. An example is a study for patients with large bowel cancer. The standard therapy for large bowel cancer is surgery. An adjuvant study could be run in which one group of patients with large bowel cancer received surgery and the other group received surgery and then chemotherapy. If the study shows that surgery plus chemotherapy is better than surgery alone, surgery plus chemotherapy will become the new, standard therapy. Adjuvant studies progress through phase I, II, and III trials like other treatment studies.

<b>Neoadjuvant studies</b><br>Neoadjuvant treatment is given first to try to reduce the cancer to a size where standard therapy is effective. For example, the standard therapy for head and neck cancer is radiotherapy and/or surgery. Sometimes the cancer is too large to safely treat by either of these methods. The chemotherapy may make the tumor shrink to a size that can be treated with radiotherapy or that can be removed surgically. Neoadjuvant studies progress through phase I, II, and III trials like other treatment studies. 

<b>Supportive care studies</b><br>Clinical trials also try to find better ways of caring for the side effects caused by cancer treatment (such as nausea and vomiting) and the side effects of the cancer itself (such as pain or sleeplessness). Some supportive care studies use drugs to treat side effects, and such studies will have phases (phase I, II, or III) like cancer therapy clinical trials. Other studies look at whether support groups help ease the discomfort of the patient. Supportive care studies sometimes try to find better ways to help the families of patients with cancer cope with the illness of a loved one. 

<b>Prevention and early detection studies</b><br>Often people in prevention studies are considered likely to develop cancer (high risk) because several family members have related cancers. Prevention studies usually compare a group of people that receive no special treatment to a group that is given a drug or a change in diet to try to prevent cancer from developing. People in both groups are contacted for many years to see if there is a difference in how many of them get cancer. Early detection studies assess methods of screening people for cancer to try to find the cancer when it is still very small. If the cancer can be found when it is small, the cancer may be more easily treated, increasing the chance for survival. These methods may use x-rays, blood tests, or touch (among others) to find cancer. Early detection studies may or may not run over many years. 

<b>Group C and Treatment Referral Center studies</b><br>These types of studies make drugs available to some cancer doctors. These drugs have been through clinical trials, have been shown to work for some tumors, and may soon be approved by the Food and Drug Administration for sale. Group C drugs can be used by a wider group of doctors than drugs used in either modified Group C or Treatment Referral Center studies. Patients who receive drugs by any of these means are checked regularly by their doctor as if they were on a clinical trial.
