Chemotherapy (chemo) uses anti-cancer drugs that are usually injected into a vein or taken by mouth. These drugs enter the bloodstream and can reach cancer that has spread. Because chemo reaches all parts of the body, it can sometimes be useful for cancers of unknown primary, as it may help kill cancer cells in areas where they haven't been detected.

Chemo can be used in a number of situations for cancers of unknown primary. If your doctor recommends chemotherapy, it's important that you understand what the goals of your treatment are.

Chemo may be the main treatment for cancers that are clearly advanced and are unlikely to be helped by local treatments such as surgery or radiation therapy. In some cases, such as with cancers that are likely to be germ cell tumors or certain types of lymphomas, it may be very effective in making tumors shrink or even go away altogether. In other cases, chemotherapy may be used more as a form of palliative therapy to try to relieve symptoms caused by the cancer.

For cancers of unknown primary that can be treated with local therapies such as surgery or radiation, chemotherapy may be added to try to kill any remaining cancer cells in the body.

Chemotherapy drugs are usually given in combinations, which are more likely to be effective than giving a single drug alone.

• For adenocarcinomas and poorly differentiated cancers where the site of origin is not clear, doctors usually recommend a combination that includes a platinum drug (cisplatin or carboplatin) and a taxane drug (paclitaxel or docetaxel). Other drugs such as gemcitabine and etoposide may also be used.

• If chemotherapy is to be used for a squamous cell cancer, the most commonly used drugs are cisplatin, 5-fluorouracil (5-FU), and a taxane (paclitaxel or docetaxel).

• For neuroendocrine carcinomas that are poorly differentiated, treatment usually includes a platinum drug (cisplatin or carboplatin) and etoposide. Well-differentiated neuroendocrine cancers are not often the cause of CUP because usually the primary site can be found. Treatment of these cancers is discussed in more detail in our documents, Gastrointestinal Carcinoid Tumors, Lung Carcinoid Tumor, and Pancreatic Cancer.

Possible side effects of chemotherapy

Chemo drugs work by attacking cells that are dividing quickly, which is why they work against cancer cells. But other cells in the body, like those in the bone marrow, the lining of the mouth and intestines, and the hair follicles, also divide quickly. These cells are also likely to be affected by chemotherapy, which can lead to side effects. Some people have many side effects, while others may have few.

The side effects of chemotherapy depend on the type of drugs, the amount taken, and the length of treatment. Some of the most common possible side effects include:

• hair loss
• mouth sores
• loss of appetite
• nausea and vomiting
• increased chance of infections (due to low white blood cell counts)
• easy bruising or bleeding (due to low blood platelet counts)
• fatigue (due to low red blood cell counts or other reasons)

These side effects are usually short-term and go away after treatment is finished. It's important to let your health care team know if you have any side effects, as there are often ways to lessen them. For example, drugs can be given to help prevent or reduce nausea and vomiting.

Several other side effects are also possible. Some of these are only seen with certain chemotherapy drugs. Your cancer care team will give you information about the possible side effects of the specific drugs you are getting. It is important to know the specific side effects that can occur with your drugs so you know what to expect and when to call your doctor.

As with other types of treatment, the chance that the benefits of chemotherapy will outweigh the downsides will depend on a number of factors, including the type and extent of the cancer and a person's general health before treatment. If you are considering chemotherapy, it's important to talk to your doctor about the chances that it will be helpful versus the likely side effects you will have.

For more information on chemotherapy, see our document, Chemotherapy: A Guide for Patients and Families.

Last Medical Review: 10/15/2009
Last Revised: 10/15/2009