A patient is considered to have a cancer of unknown primary origin when cancer is detected at one or more sites and routine evaluation fails to identify the primary tumor. Cancer of unknown primary constitutes up to 7% of all cancers and poses a therapeutic dilemma because cancer treatment is typically determined by the specific primary tissue of origin.
Because the most common causative primary tumors are those of the testes, lungs, colon and rectum, and pancreas, examination of these areas must be thorough.
Types of testing used to help identify the primary tumor include
Laboratory testing
Imaging tests
Immune cytochemical and immune peroxidase staining
Tissue analysis
Laboratory tests should include a complete blood count (CBC), urinalysis, stool examination for blood, and serum chemistries (including prostate-specific antigen assay in males).
Imaging should be limited to a chest x-ray, abdominal CT, and mammography. Endoscopic examination of the upper and lower gastrointestinal tract should be done if blood is present in the stool.
Tissue analysis for estrogen and progesterone receptors helps identify breast cancer, and immunoperoxidase staining for PSA (prostate-specific antigen) helps identify prostate cancer.
< 1 year).