One major feature of cancers is that it can develop anywhere within the body. The organs or a region of the body where cancer develops is referred to as the primary site. Cancer - including those types of cancer that metastasizes or spreads, to create new tumors elsewhere in the body - is called the primary site. Takes for instance colon cancer which spreads to other parts of the body such as the liver is referred to as metastatic colon cancer rather than liver cancer because it contains colon cancer cells.

According to the American Cancer Society, about 2 to 5 percent of all cancer patients possess metastatic (secondary) tumors for which routine examination find it difficult to locate the primary site. This is generally referred to as cancer of the Unknown Primary Origin (UPC). Patients can be diagnosed with cancer of unknown primary origin in the event that the primary tumor is too small to be discovered with routine imaging tests, it disappears before the appearance of the secondary tumor, or secondary tumors have several possible primary sites. Sometimes the primary tumor is discovered during the surgery that is meant to treat other conditions.

The cancer of an unknown primary origin can occur anywhere in the body but most commonly occurs in the lymph nodes, liver, lungs, bones or skin.

Types of Cancer of Unknown Primary Origin

Cancer of Unknown Primary Origin is divided into four types. The pathologist can determine the type of cancer by observing tumor cells with the use of a microscope.

  • Adenocarcinoma
  • Poorly differentiated cancer
  • Squamous cell carcinoma
  • Neuroendocrine carcinoma

Diagnosis of Cancer of Unknown Primary Origin

Since the cancer of unknown primary origin is metastatic cancer (cancer that has spread from one part of the body to the other), it is already considered advanced. Physicians can first try to find a primary site, but for many patients, they will never find it. In the event that the primary site cannot be discovered, the diagnosis will focus on determining the location (s) of cancer and cell types that make up the tumor to develop a treatment plan.

Sometimes doctors can identify a primary site with certainty based on a particular combination of factors:

  • In women, an adenocarcinoma in the lymph node below the arms often shows breast cancer. Mammograms and breast examination can help to diagnose this type of cancer.
  • In young men, abdominal tumors may suggest testicular cancer.
  • Head and neck cancer is usually the major source of pancreatic cancer in the upper body or lymph nodes.
  • Cholangiocarcinoma (gallbladder cancer) can be the main source of a liver tumor.
  • Prostate, penile or anal cancer may be the primary site for men with cancer in the lymph node of the groin. In women, increased lymph nodes in the groin can indicate cervical or vaginal cancer.
  • In women, ovaries may be the primary site for adenocarcinoma in the abdomen.

For most patients, doctors depend on the information obtained from blood tests, imaging studies, and pathological tests to learn more about the tumor.

Treatment of cancer of unknown primary origin

Since the cancer of unknown primary origin is regarded by definition as cancer that has spread to other parts of the body from the primary site, the disease is already in the advanced stage until the time it is diagnosed. Although there is no standard treatment for CUP tumors, chemotherapy is usually the main treatment.

Chemotherapy and Biological Therapy

The most common treatment for patients affected with cancer of unknown primary origin is chemotherapy. Administered intravenously or orally, chemotherapy destroys cancer cells throughout the body, including areas that have not yet been detected. This approach is used to reduce tumors and relieve symptoms of cancer. In rare cases, chemotherapy can remove tumors so there is no need for additional treatment.


Surgery is often a treatment for people with a primary tumor limited to the organs where it started. But since cancer of unknown primary origin has already expanded, surgery is usually not effective. In rare cases, when a CUP tumor is detected in one organ or lymph node, surgery may be the best option which is recommended by your doctor. If cancer is thought to have started in the breast, mastectomy (surgical removal of the breast) may be necessary to ensure that all breast cancer cells are removed. When surgery is used to treat cancer of unknown primary origin, it is usually followed by chemotherapy or radiation therapy to remove all remaining cancer cells.

Other treatments

Radiotherapy used only for tumor control which cannot be removed with surgery or when cancer of unknown primary origin spreads to the spinal cord and impairs neurological functions. Hormone therapy is another option used to treat patients whose cancer probably started in the breast or prostate.

Other options for treating cancer of unknown primary (CUP) may include:

  • Hormone Therapy for a Cancer of Unknown Primary
  • Targeted Therapy for a Cancer of Unknown Primary

Other Drugs for a Cancer of Unknown Primary

Cancer of Unknown Primary

Cancer of Unknown Primary

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