What are primary tumors

Tumor metastases in an unknown primary tumor


Robert Peter Gale

, MD, PhD, Imperial College London

Content last changed Jul 2018
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A patient is considered to have a cancer of unknown primary origin if cancer is detected in one or more sites and routine evaluation does not identify the primary tumor. Cancer of the unknown primary cancer accounts for up to 7% of all cancers and represents a therapeutic dilemma since cancer treatment is typically determined by the specific primary tissue of origin.

Since the most common causative primary tumors are the testes, lungs, colon and rectum, and pancreas, these areas must be examined thoroughly.

The types of tests used to identify the primary tumor include, but are not limited to

  • Immunocytochemical and immunoperoxidase stains

Laboratory tests should include a complete blood count, urinalysis, stool test for blood, and serum chemistry (including prostate-specific antigen in men).

Imaging should be limited to chest x-ray, abdominal CT, and mammography. An endoscopic examination of the lower and upper gastrointestinal tracts should be done if there is blood in the stool. (Editor's note: In Germany, a colonic contrast enema has been replaced by a colonoscopy.)

The increasing number of immunocytochemical staining of available tumor material may make it possible to identify the primary tumor tissue; tumors that arise in the lungs, colon, or breast can also be identified. In addition, immunoperoxidase staining for immunoglobulin, chromosomal studies, and immunophenotyping can help diagnose the various subtypes of malignant lymphomas, which can be difficult to identify and differentiate from other tumors (even carcinomas) outside the lymph nodes. human chorionic gonadotropin may indicate easily treatable germ cell tumors.

Tissue examinations for estrogen or progesterone receptors are useful in identifying breast cancer and immunoperoxidase staining for prostate-specific antigen in prostate cancer.

Even if a precise histological diagnosis is not possible, a constellation of the examination results can indicate a place of origin. Poorly differentiated carcinomas near the midline of the mediastinum or retroperitoneum in young or middle-aged male patients suggest a germ cell tumor, even in the absence of a testicular mass. Patients with this type of cancer should be treated with a cisplatin-based procedure since nearly 50% have long disease-free intervals. In most tumors with an unknown primary tumor, the response to this or other polychemotherapy regimen is usually only moderate and of short duration (median survival <1 year).

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