Carcinoma of Unknown Primary Health Article

Definition

Carcinoma of unknown primary (CUP) is a disease in which malignant (cancerous) cells are found in the body, but the organ where they initially began growing, the primary site, cannot be discovered.

Description

The area where a cancer originates in the body is often referred to as the primary tumor. Cancer of unknown primary is a cancer that starts out in an unknown spot and then metastasizes (spreads) to another site, such as a lymph node, the liver, lung, brain, or the bones. Because the primary site is unknown, prognosis may differ from patient to patient.

Most cancers are named after the area of the body in which they start. For example, breast cancer is cancer that originates in the breast. If it spreads to another part of the body, it is still called breast cancer, and the cancerous cells that have metastasized still look like breast cancer cells. With CUP, however, doctors are unable to know with certainty the origin of these cells.

Demographics

According to the American Cancer Society, about 35, 000 cases of cancer of unknown primary are diagnosed each year. These represent approximately 3% to 5% of all cases of cancer. The average age of a patient diagnosed with CUP is approximately 58. The disease is more common in men than in women.

Causes and symptoms

Every cancer has distinct risk factors, or causes. It is difficult to identify specific causes of CUP since the exact type of cancer is unknown.

The symptoms of carcinoma of unknown primary are organ-specific. These symptoms may include:

• Lymphadenopathy, a condition in which the lymph nodes are swollen, firm to the touch, but do not hurt. Cancers frequently spread to the lymph nodes.
• A mass in the abdomen or a feeling of abdominal fullness. This is often caused by a cancer growing in the liver or the spleen, or by a collection of fluid inside the abdomen called ascites.
• Shortness of breath. This symptom may be caused by cancer that has spread to the lungs or from pleural effusion, a build-up of fluid and cancer cells in the area around the lungs.
• Pain in the chest or abdomen. Cancer growth around nerves or tumors pressing against internal organs may cause these symptoms.
• Bone pain. Severe pain may occur when cancer has spread to the bones. Bones that are made weak by the cancer's spread may contribute to fractures. These fractures may result from minor injuries, or even from normal activities, like rolling over in bed.
• Skin tumors. Some cancers start out in organs and spread through the bloodstream to the skin. Skin metastases are sometimes the first sign of spread from a cancer of unknown primary.
• Weakness, fatigue, poor appetite, and weight loss. These generalized symptoms may happen because the cancer has spread to specific organs or systems. Also, some cancers release hormone-like substances into the bloodstream that affect metabolism and cause these same problems.

Diagnosis

The initial step in evaluating a person with cancer is a medical history and general physical exam. These simple steps may suggest the origin of the cancer. If this is not apparent, various imaging tests, blood tests, and endoscopic exams may be used. A biopsy would be performed for routine study under the microscope. The biopsy is the most important of these tests, as it is needed to confirm the diagnosis of cancer. Once the presence of cancer is confirmed, the doctor will then attempt to find its source. Selecting which tests to perform is dependent upon which cancers are likely to occur in a person of the patient's age and gender.

Many of the tests done on a patient with CUP are geared towards finding the primary site. Blood cell counts and blood cell examination will be performed, because changes in the numbers of different blood cell types may suggest that a cancer of unknown primary has spread to the bones. Another type of blood test commonly done at this diagnostic stage is the serum tumor marker, which measures the amount of substances that are secreted by some cancers into the bloodstream. If these substances are present in the blood of patients with CUP, they can provide clues to the origin of the cancer.

The next diagnostic step is usually a biopsy. The samples obtained for the biopsy will undergo various laboratory tests to help place the cancer into a category that will guide the doctor in choosing appropriate treatment. In addition to biopsies, various imaging studies may be performed to produce pictures of the inside of the body. X rays are often done to determine the presence of a mass, but they are not usually useful in finding out what type of cancer is present or in what organ it began. A computed tomography (CT) scan is often done to produce a detailed picture of the inside of the body, and can often depict the amount of cancer spread throughout the body. CT scans also aid in finding primary tumors in the throat, sinuses, pancreas, ovaries, and some other organs. Magnetic resonance imaging (MRI) takes pictures similar to, but more detailed than, the CT scan. Ultrasounds may show which organs have been affected by CUP, but only rarely can they help find the cancer's site of origin.

In order to receive a diagnosis of cancer of unknown primary, the patient must have had the following done in an attempt to find the origin:

• complete medical history and physical exam
• complete blood cell count and routine blood chemistry tests
• biopsy of the metastatic tumor with a microscopic examination of the cancer cells, along with certain other tests
• if the tumor is found in the abdomen or in the lymph nodes of the groin, a chest x ray and CT scan of the abdomen and pelvis
• ultrasound of the testicles (in males) or pelvis (in females)
• mammogram
• routine testing of the urine
• testing of the stool for blood, which may indicate cancer of the digestive system
• examination of the gastrointestinal (GI) tract
• thyroid scan

If all of these examinations are done, and the primary tumor site is still undetermined, then the patient is given the diagnosis of carcinoma of unknown primary. Based on the cancer's location and classification, doctors will determine which additional tests should be performed.