Unknown Primary: Subtypes

Approved by the Cancer.Net Editorial Board, 03/2015

ON THIS PAGE: You will find descriptions of the most common types of CUP tumors. To see other pages, use the menu on the side of your screen.

Most people with CUP have one of four types of tumors:

  • Adenocarcinoma. Nearly 60% of people with CUP have adenocarcinoma. Adenocarcinoma can develop in the glandular tissue of most internal organs, including the lungs, stomach, pancreas, colon, ovary, and breast. Because of this, it is extremely difficult for a pathologist to tell where an adenocarcinoma began when it is found at a metastatic site.

    Additional diagnostic tests on biopsy samples, called IHC stains, usually narrow down the possibilities and can predict the primary site about 30% to 40% of the time. A molecular cancer classifier assay of the biopsy specimen can accurately predict the primary site for most remaining patients. Learn more about molecular tumor profiling in the Treatment Options and Latest Research sections.

  • Poorly differentiated carcinoma. Nearly 20% to 30% of people with CUP have poorly differentiated carcinomas. Pathologists do extra testing on biopsy samples of these tumors because some very treatable cancers may initially be diagnosed as poorly differentiated carcinoma. Similarly to patients with adenocarcinoma, a molecular cancer classifier assay can usually predict the site of tumor origin and is useful in guiding the choice of therapy. If this testing shows the cancer is lymphoma, germ cell carcinoma, or neuroendocrine carcinoma, effective treatments are often available.
  • Squamous cell carcinoma. About 5% to 10% of people with CUP have squamous cell carcinoma. If squamous cell carcinoma is found in the cervical lymph nodes in the neck, the primary site is often in the head and neck area. If it is found in the inguinal lymph nodes in the groin, the primary site may be in the vulva, vagina, cervix, anus, or bladder. A careful search is important, especially since these cancers can often be treated successfully.
  • Neuroendocrine carcinoma. Approximately 1% to 5% of people with CUP have neuroendocrine carcinoma. These cancers are being found more often with IHC tests. Some of these tumors are aggressive and fast growing, but combination chemotherapy (see the Treatment Options section) may be effective. Others are very slow growing, and people sometimes live for several years even without treatment.

Information about the tumor’s subtype will help the doctor recommend a specific treatment plan. The next section in this guide is Treatment Options. Or, use the menu on the side of your screen to choose another section to continue reading this guide.