Approximately 3 percent of cancer diagnoses are Occult Primary Adenocarcinoma. Despite its ominous-sounding name, this diagnosis simply means physicians cannot determine in what part of the body a patient's cancer originated. It's more commonly called Carcinoma of Unknown Primary (CUP).

Cancer Diagnosis by Site of Tumor Origin
Cancer is really a collection of more than 100 different diseases. Tumors typically begin in a specific area of the body, such as the breast, prostate, or lung. Physicians diagnose these as primary tumors based on their place of origin, which they can often determine by looking at the cancer cells under a microscope, since cancer cells look different based on where in the body they originate. When cancers spread to other parts of the body, the resulting tumors are known as secondary cancers. Nonetheless, the diagnosis does not change: For example, if breast cancer cells spread to the brain, the patient still has breast cancer.

Occasionally, despite extensive diagnostic evaluation, sometimes the origin of the tumor remains elusive; CUP tumor features are simply not specific enough to determine the site of origin. Sometimes primary tumors are small and slow-growing, making it difficult to discern where they began. In 15 to 25 percent of cases, the primary site remains a mystery, even after postmortem examination. There are several possible reasons for this.  For instance, the immune system may have killed the primary tumor, or a physician unknowingly removed it during an unrelated surgery.

Sixty to 70 percent of all CUPs begin in one of the body's glands, making them adenocarcinomas. Historically, up to half of these cancers originate in the pancreas, lung, or bile ducts; other gastrointestinal sites are also common. Most patients with adenocarcinomas have tumors in more than one location in the body. Despite being common types of cancer, most adenocarcinomas are not breast or prostate cancers.

Risk Factors and Symptoms
The risk factors for CUP mirror those of most other cancers:

  • Age
  • Exposure to chemicals or the sun
  • Poor nutrition
  • Lack of exercise
  • Family history

CUP symptoms generally occur in the area near the tumor and may include:

  • Long-lasting pain in a specific area
  • Loss of appetite or unexplained weight loss
  • Persistent cough or hoarseness
  • Thickening of an area or a lump
  • Changes in bladder or bowel habits
  • Unusual bleeding or discharge
  • Recurring fever or night sweats

Projected outcome for patients with CUP is generally poor. However, scientists are continually learning more about these cancers. If you have CUP, ask your physician about participating in clinical trials.


National Cancer Institute. "Carcinoma of Unknown Primary Treatment (PDQ®)." Web. 22 February 2012.

National Center for Biotechnology Information. "Adenocarcinoma of Unknown Primary Site." Web.

Cancer Net. "Unknown Primary." Web. 26 March 2012.

National Cancer Institute. "Carcinoma of Unknown Primary Treatment (PDQ®)." Web. 27 September 2011.

Mulcahy Nick. "Molecular Test Aids in Identifying Cancers of Unknown Origin." Medscape Medical News. Web. 22 July 2011.