Unknown Primary: Subtypes

Approved by the Cancer.Net Editorial Board, 03/2014

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 may begin in the glandular tissue of most internal organs, including the lungs, stomach, pancreas, colon, ovary, and breast. Because of this, when adenocarcinoma is found at a metastatic site, it is extremely difficult for the pathologist to tell where it began. Additional diagnostic tests on biopsy samples, called IHC stains, usually narrow down the possibilities and can predict the site of origin in about 30% to 40% of patients. A molecular tumor profiling assay that is also performed on the biopsy specimen is able to accurately predict the site of origin in 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. These cancers need to undergo extra testing by the pathologist, since some very treatable cancers may initially be diagnosed as poorly differentiated carcinoma. If testing finds the cancer is lymphoma, germ cell carcinoma, or neuroendocrine carcinoma, effective treatments are often available. Similarly to patients with adenocarcinoma, molecular tumor profiling can usually predict the site of tumor origin and is useful in guiding the choice of therapy (see the Treatment Options section).

Squamous cell carcinoma. Nearly 5% to 10% of people with CUP have squamous cell carcinoma. Effective treatments are available for this type of tumor if it has certain characteristics. For instance, if squamous cell carcinoma is found in the cervical (neck) lymph nodes, the primary site is often in the head and neck area. If it is found in the inguinal (groin) lymph nodes, the primary site may be in the vulva, vagina, cervix, anus, or bladder. A careful search is important, particularly since these cancers can often be treated successfully.

Neuroendocrine carcinoma. Nearly 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 treatment plan. The next section helps explain the treatment options for this type of cancer. Use the menu on the side of your screen to select Treatment Options, or you can select another section, to continue reading this guide.