Chemotherapy uses anti-cancer drugs that are injected into a vein or given by mouth as pills. These drugs enter the bloodstream and reach all areas of the body, making this treatment useful for cancer that has spread to organs beyond the stomach.

Chemotherapy may be given as the primary (main) treatment for stomach cancer that has spread to distant organs. It may help relieve symptoms for some patients, especially those with spread (metastases) to other areas of the body. It may also help some patients live longer.

Chemotherapy is also used as an adjuvant treatment (given after surgery) along with radiation therapy for some stages of stomach cancer. This combination is called chemoradiation. It may delay cancer recurrence and extend the life span of people with less advanced stomach cancer, especially if their cancer could not be removed completely by surgery.

The use of chemotherapy as a neoadjuvant treatment (given before surgery) in some situations is still being studied.

Chemotherapy for stomach cancer may use one drug such as 5-fluorouracil (5-FU), which is often combined with radiation therapy. Or chemotherapy may use several drugs combined. The most commonly used drugs are 5-FU, doxorubicin, methotrexate, etoposide, and cisplatin. Other drugs that may be helpful are docetaxel, irinotecan, capecitabine, and oxaliplatin. It is not yet clear which drugs or combinations of drugs work best against stomach cancer.

Chemotherapy drugs kill cancer cells but also damage some normal cells, which can lead to side effects. The type of side effects depends on the type of drugs, the amount taken, and the length of treatment. Short-term side effects might include nausea and vomiting, loss of appetite, hair loss, diarrhea, and mouth sores. Because chemotherapy can damage the bone marrow, where new blood cells are made, your blood cell counts might become low. This can result in:

• increased chance of infection (due to a shortage of white blood cells) 
• bleeding or bruising after minor cuts or injuries (due to a shortage of platelets) 
• fatigue and shortness of breath (due to low red blood cell counts)

Most side effects go away once treatment is stopped. For example, hair will usually grow back after treatment ends.

It is important to talk to your doctor or nurse about any side effects you have. There are treatments that can help reduce them or make them go away. For example, drugs can be given to help to prevent or reduce nausea and vomiting.

Targeted therapies: Newer drugs, which target specific parts of cancer cells, are now being tested against stomach cancer. Some of these are discussed in more detail in the section "What's New in Stomach Cancer Research and Treatment?"