Imagine being told that you have cancer in one or several regions of your body but that the doctors cannot determine where it started. In other words, you have metastatic cancer without a corresponding primary tumor to indicate where the cancer began.
The liver, bones, lungs, lymph nodes, or other areas may be affected but in a way that indicates that the cancer spread to them from some other primary location. Investigation of the breast, prostate, lungs, gastrointestinal tract, and other organs, however, fails to reveal the tumor of origin.
People who have this perplexing and frightening condition frequently request that a total body CT scan be performed in an effort to locate the primary tumor. Often, however, a full-body CT scan, an MRI, and even a PET scan cannot locate the primary cancer. Patients may seek numerous opinions and go to the biggest cancer hospitals in the hope that some doctor will be smart enough to figure out where the cancer began.
These efforts are natural and thoroughly understandable. In the end, however, neither a sophisticated test nor the most skilled physician will be able to uncover the cancer source. The diagnosis will remain carcinoma of unknown primary site (CUP).
Carcinoma of unknown primary site is not on the list of the most common cancers. I have yet to hear it mentioned in the news, and I have never met a new patient who was familiar with it. One would think it is a rare type of cancer. Yet surprisingly, CUP accounts for approximately 5 percent of cancers, making it a disease that oncologists are quite familiar with.
This type of carcinoma has been the subject of many clinical trials and has been studied by cancer researchers for many years. There are standardized ways of treating it in all its manifestations. Patients with CUP must suffer the anguish of battling a cancer they cannot understand and cannot easily describe. Most tell others that they have “bone cancer,” “liver cancer,” or another type depending on where the disease is most burdensome; to describe CUP invites questions and doubts about the diagnosis. Some CUP patients I care for ask me at nearly every office visit to explain their cancer again and to review once more where it could possibly have come from. CUP is not only an enor mously frustrating cancer but also a lethal one, with average survivals of less than two years.
Most cases of CUP are thought to represent the metastases of a carcinoma that either completely shrank away (involuted) or is too small to be detected by current methods. Pathologists will perform numerous tests on the cancer specimen to try to determine its origin. When such tests fail to identify an organ of origin, the diagnosis is CUP. It is hoped that sophisticated genetic analyses of CUP tumors will yield more accurate ways of classifying them; these tests are undergoing validation in clinical trials.
Cancers of unknown primary site are usually treated with chemotherapy and sometimes also with radiation therapy. Some patients can be cured if the cancer is localized and not disseminated in the body, in which case surgery may play a role. Better treatments are clearly needed for advanced cases of CUP. Researchers are trying to gain a better understanding of how CUP develops so that greater strides can be made against this cancer.
