Cancer of unknown primary is a disease that has metastasized (spread) from another part of the body. The place where it began, also called the primary site, is unknown. These cases make up about 2% to 5% of cancers diagnosed in the United States. Thanks to better diagnostic tests, though, they are becoming less common.
About four of every five cases that are first diagnosed as cancer of unknown primary eventually are confirmed to be specific types of cancer. CUP most often is found in the lymph nodes, liver, lung, peritoneum (lining of the bowel) or bone.
Cancer of unknown primary often is challenging because it tends to be aggressive and has often spread to many parts of the body before it is found. In addition, because origin of cancer is unknown, it may be more challenging to choose the best treatment.
Cancer of Unknown Primary Types
Although doctors are at first unable to determine where CUP began, they study the cancer to find out as much as possible about them. After looking at the cancer cells under a microscope, they usually decide the cancer belongs in one of the following categories:
Adenocarcinomas: About six of every 10 cancer of unknown primary cases are adenocarcinomas, meaning they began in gland cells. Most frequently, the primary sites are the lung, pancreas, breast, prostate, stomach, liver or colon.
Poorly differentiated carcinoma: Cancer cells are present, but they do not have enough detail for doctors to decide the type of cancer. Around 10% of these CUP cases are found to be lymphoma, melanoma or sarcoma.
Squamous cell cancer: The cells are flat, similar to cells on the skin or linings of some organs.
Poorly differentiated malignant neoplasm: Cells are definitely cancer, but they are so abnormal it cannot be determined what type of cell or part of the body they began in. Sometimes they are lymphomas, sarcomas or melanomas.
Neuroendocrine carcinoma: This type of CUP begins in the neuroendocrine system, making the cells like nerve cells and hormone-making cells. They are scattered in organs including the esophagus, stomach, pancreas, intestines and lungs.
CUP Risk Factors
Because the primary site of many cancer of unknown primary cases is never found, it is difficult to say what causes them. In the cases in which the primary site is determined, possible risk factors are based on that type of cancer.
- Smoking tobacco is a risk factor in cancers of the pancreas, lungs, kidney, throat, larynx and esophagus. More than half of people with CUP have used tobacco.
- Diet and being overweight are linked to cancers that begin in the stomach, colon or rectum.
- Too much sun exposure causes some melanomas.
However, it has not been proven that any of these factors make a person more likely to develop cancer of unknown primary.
Learn more about cancer of unknown primary:
Why choose MD Anderson for cancer of unknown primary care?
At MD Anderson’s Gastrointestinal Center, we have the depth of expertise to provide customized treatment for each patient with cancer of unknown primary (CUP). Our pathology experts have significant experience in evaluating cancer of unknown primary. We use advanced diagnostic methods to pinpoint the origin of CUP tumors, which are then treated by a team of renowned specialists.
Our experts work together in specialized teams that focus an incredible level of knowledge on you. Using the latest, most advanced technology, MD Anderson’s pathologists have extraordinary skill in diagnosing the origin of cancer of unknown primary.
Advanced Treatment, Range of Support
If the site of origin of cancer of unknown primary is found, MD Anderson offers a full range of the most advanced treatments for every diagnosis. Depending on the type of cancer, these may include proton therapy, targeted therapies, surgery and others.
As one of the world’s leading cancer centers, we offer a range of clinical trials of new therapies. And because we know CUP can take a toll on you and your family’s quality of life, we provide a range of support and wellness services to help you live your life to the fullest. This includes specially trained psychologists and a supportive care team who know what you are going through and can help.
