Cancer of unknown primary origin (CUP) is a
cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
that is determined to be at the
metastatic
Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, ...
stage at the time of diagnosis, but a
primary tumor A primary tumor is a tumor growing at the anatomical site where tumor progression began and proceeded to yield a cancerous mass. Most cancers develop at their primary site but then go on to metastasize or spread to other parts of the body. These fur ...
cannot be identified. A diagnosis of CUP requires a clinical picture consistent with metastatic disease and one or more
biopsy
A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a dise ...
results inconsistent with a tumor cancer
CUP is found in about 3 to 5% of all people diagnosed with invasive cancer,
and carries a poor
prognosis in most (80 to 85%) of those circumstances. The other 15 to 20% of patients, however, have a relatively long survival with appropriate treatment.
Signs and symptoms
Most cancers typically present as a single
primary tumor A primary tumor is a tumor growing at the anatomical site where tumor progression began and proceeded to yield a cancerous mass. Most cancers develop at their primary site but then go on to metastasize or spread to other parts of the body. These fur ...
. Over the course of time—particularly if the primary tumor is left untreated—smaller "satellite" tumors will appear at other places in the body, a phenomenon known as
metastasis
Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then ...
. Less commonly, a metastatic tumor is found first; but in most such cases, the primary tumor can then be located via examination and testing. Rarely (3-5% of the time), the primary tumor cannot be found because it is too small, or because it has
regressed due to
immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...
activity or other factors. In such situations a diagnosis of cancer of unknown primary origin (CUP) is made.
CUP usually comes to attention because of masses or swellings found somewhere in the body, either by
physical examination
In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally consists of a series of questions about the pati ...
or on
medical imaging performed for another indication. The disease typically develops rapidly, and metastases may occur in places in the body that are otherwise unusual.
Comprehensive physical examination is part of the process to identify a possible primary source of cancer; this should include the
breast
The breast is one of two prominences located on the upper ventral region of a primate's torso. Both females and males develop breasts from the same embryological tissues.
In females, it serves as the mammary gland, which produces and sec ...
s,
lymph nodes, the
skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other animal coverings, such as the arthropod exoskeleton, have different de ...
, external genitals, as well as an
internal examination of the rectum and
of the pelvic organs.
The location of metastases may be a clue as to the underlying source, even if this cannot be found on investigations. For instance, a woman in whom there is
axillary lymphadenopathy (swelling in the
lymph nodes of the armpit) it is likely that the
cancer originated in the breast, and men with lymph node deposits in the
mediastinum of the chest and/or
retroperitoneal space
The retroperitoneal space (retroperitoneum) is the anatomical space (sometimes a potential space) behind (''retro'') the peritoneum. It has no specific delineating anatomical structures. Organs are retroperitoneal if they have peritoneum on thei ...
of the abdomen may have a
germ cell tumor.
[
]
Mechanism
Cancer of unknown primary source is not a single type of cancer, although researchers have attempted to find a common characteristic that explains why a cancer might spread very early without causing symptoms at the site of origin.[ It is generally accepted that cancer of unknown primary site exists because the primary tumor is not identified due to clinical or technological inefficiencies, or because the primary tumor regresses or stays dormant after spreading the cancer cells that generate the metastases. This view is widely accepted in oncology; in fact, these cancers are also referred to as occult primary tumors. Because the site of the primary tumor usually dictates the treatment and expected outcome, this view may help create uncertainty and anxiety among health professionals and patients, who may feel that their evaluation has been incomplete.
Because stem cells have a natural ability to migrate and also play a key role in cancer development, it has been proposed that a cancer of unknown primary site may form when deregulated, premalignant or cancerous stem cells migrate away from their natural tissue and give rise to a cancer in the new site before or without generating a tumor in their original tissue.] Forming a tumor in a tissue is not a prerequisite for stem cells to move away from that tissue. Stem cells can migrate from their natural tissue and initiate a cancer in the new site before generating a detectable tumor in their natural tissue. In this case, the primary tumor could be identified after some time. However, stem cells can also migrate away from their natural tissue without generating a cancer there. In this case, the "primary tumor" would never exist (se
Figure
. This can explain why the primary site is not identified even on postmortem examination in many patients with these cancers.[ This view of CUP may provide relief to health professionals and patients. After a detailed imaging and pathologic analysis, oncologists can tell their patients with CUP that metastasis does not always involve the formation of a primary tumor, and that their diagnostic evaluation is complete.][
]
Diagnosis
In recent years, microscopic and other diagnostic techniques have improved dramatically. However, the tissue of origin can be still determined only about in one in four cases of CUPs with these methods. In some cases, the part of the body where cancer cells are first discovered helps the doctor decide which diagnostic tests will be most helpful. Additional clues which may be helpful in determining the primary site include the pattern of spread, and the cell type, which is based on its appearance under a microscope (histology
Histology,
also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vi ...
).
The initial work-up of a cancer of unknown primary includes a CT scan of the chest, abdomen, and pelvis, with IV contrast. Women with enlarged lymph nodes ( lymphadenopathy) confined to the axillary region with CUP should have a mammogram
Mammography (also called mastography) is the process of using low-energy X-rays (usually around 30 Peak kilovoltage, kVp) to examine the human breast for diagnosis and screening. The goal of mammography is the early detection of breast cancer, ty ...
or ultrasound
Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies ...
to evaluate for possible breast cancer. If those imaging studies are normal, then an MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
of the breast may be appropriate. A PET CT scan should be done for squamous cell carcinoma involving lymph nodes of the neck region. For other types of cancer of unknown primary, a PET-CT offers uncertain benefit.
The pattern of spread may suggest the location of the primary site. For example, metastatic cancer found in the upper body is more likely to have an origin above the diaphragm, at sites such as the lung and breast. If the metastatic cancer appears first in the lower part of the body, the primary cancer is more likely to be at sites below the diaphragm, such as the pancreas and liver.
When the cancer cells are poorly differentiated (that is, they look less evolved than normal cells when viewed under a microscope), the cancer may be either a lymphoma or a germ cell tumor. Lymphomas begin in the lymphatic system. Germ cell tumors usually begin in the ovaries and testes. In patients in whom the primary cancer is eventually found, the lung and pancreas are the most common primary cancer sites. CUP also may be traced to the breast, prostate, colon, or rectum as the primary site.
Sometimes, however, even when doctors use very sophisticated methods to try to identify the primary site, the part of the body the cancer cells came from cannot be determined. About 2 to 4 percent of all cancer patients have a cancer whose primary site is never found. Identifying the primary tumor site is important because knowing its location and type often helps doctors plan the best treatment. Treatment that is specific to the suspected type of cancer is likely to be more effective. Still, when diagnostic tests have not identified the primary site, doctors must decide whether the potential benefits of more extensive testing outweigh a patient's discomfort, possible complications, and the financial costs.
Immunohistochemical testing
Antibodies may be used to determine the expression of protein markers on the surface of cancer cells. Often the expression of these antigens is similar to the tissue that the cancer grew from, so immunohistochemical testing sometimes helps to identify the source of the cancer. Individual tests often do not provide definitive answers, but sometimes patterns may be observed, suggesting a particular site of origin (e.g. lung, colon, etc.). Immunohistochemical testing suggests a single source of cancer origin in about one in four cases of CUP. However, there is a lack of definitive research data showing that treatment guided by information from immunohistochemical testing improves outcomes or long-term prognosis.
Classification
CUP may be classified by its appearance under a light microscope. The majority of cancers of unknown primary, about 90%, are adenocarcinomas, with 60% appearing as moderately to well- differentiated adenocarcinoma, while about 30% are poorly differentiated adenocarcinoma. The term ''adenocarcinoma'' refers to cancer that begins in the cells in glandular structures in the lining or covering of certain organs in the body. Common primary sites for adenocarcinomas include the lung, pancreas, breast, prostate, stomach, liver, and colon.
The remaining 10 percent are either poorly or undifferentiated malignant neoplasms (5%), or squamous cell carcinomas (5%). Rarely, CUP may appear as neuroendocrine tumors, or mixed tumors, such as sarcomatoid, basaloid, or adenosquamous carcinomas.
Management
Because CUP refers to many different cancers, treatment depends on where the cancer is found, the microscopic appearance of the cancer cells, the biochemical characterization of the cells, and the patient's age and overall physical condition. In women, who present with axillary lymph node involvement, treatment is offered along the lines of breast cancer. In patients, who have neck lymph node involvement, then treatment is offered along the lines of head and neck cancer. If inguinal lymph nodes are involved, then treatment may be offered along the lines of genitourinary cancer.
If the site of origin is unknown or undiscovered, then the histology of the tumor (e.g., adenocarcinoma, squamous cell or mesenchymal) can usually be identified, and a probable origin may be assumed. When this is possible, then treatment is based on the type of cell and probable origin. Based on histological subtype, combination chemotherapy may be selected. A combination of carboplatin
Carboplatin, sold under the trade name Paraplatin among others, is a chemotherapy medication used to treat a number of forms of cancer. This includes ovarian cancer, lung cancer, head and neck cancer, brain cancer, and neuroblastoma. It is used b ...
and paclitaxel
Paclitaxel (PTX), sold under the brand name Taxol among others, is a chemotherapy medication used to treat a number of types of cancer. This includes ovarian cancer, esophageal cancer, breast cancer, lung cancer, Kaposi's sarcoma, cervical canc ...
is often used. Advances techniques such as FISH
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...
and tissue of origin testing may also be employed. Germ cell tumors often carry abnormality of chromosome 12
Chromosome 12 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 12 spans about 133 million base pairs (the building material of DNA) and represents between 4 and 4.5 percent of the to ...
, which if identified, directs treatment for metastatic germ cell tumors.
No method is standard for all forms of CUP, but chemotherapy
Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemothe ...
, radiation therapy
Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radi ...
, hormone therapy, and surgery may be used alone or in combination to treat patients who have CUP. Even when the cancer is unlikely to be cured, treatment may help the patient live longer or improve the patient's quality of life. Radiation may be used to shrink a variety of local tumors. However, the potential side effects of the treatment must be considered along with the potential benefits.
In CUP to secondary neck nodes, surgery followed by external beam radiotherapy is sufficient.
For CUP with an unfavorable prognosis, treatment with taxane
Taxanes are a class of diterpenes. They were originally identified from plants of the genus ''Taxus'' (yews), and feature a taxadiene core. Paclitaxel (Taxol) and docetaxel (Taxotere) are widely used as chemotherapy agents. Cabazitaxel was FDA ap ...
s may provide a slight survival benefit. The uncertainties and ambiguity inherent in a CUP diagnosis may cause additional stress for the patient.
Prognosis
Most people with cancer of unknown primary origin have widely disseminated and incurable disease, although a few can be cured through treatment. With treatment, typical survival with CUP ranges from 6 to 16 months. Survival rates are lower in cases with visceral metastatic disease, ranging from 6 to 9 months. Survival rates are higher when the cancer is more limited to lymph nodes, pleura, or peritoneal metastasis, which ranges from 14 to 16 months. Long-term prognosis is somewhat better if a particular source of cancer is strongly suggested by clinical evidence.
Epidemiology
CUP sometimes runs in families. It has been associated with familial lung, kidney, and colorectal cancers, which suggests that these sites may often be the origin of unidentifiable CUP cancers.
UK
Around 9,800 people were diagnosed with cancer of unknown primary in the UK in 2011, and around 10,625 people died from the disease in 2012.
History
From 1980 to 1990, definition of unknown primary cancer was based on imaging results. Subsequently, research on immunohistochemistry allowed for the classification of cancer of unknown primary into sub-types. From 2000 to 2010, tailored therapies began to evolve, targeting specific subtypes of unknown primary.
Further reading
*
*
References
External links
*
Clinically reviewed information on unknown primary cancer
for patients, from Cancer Research UK
Cancer Research UK (CRUK) is the world's largest independent cancer research organization. It is registered as a charity in the United Kingdom and Isle of Man, and was formed on 4 February 2002 by the merger of The Cancer Research Campaign and t ...
The CUP Foundation - Jo's Friends
- UK-based information and support for patients with CUP.
Cancer.Net: Unknown Primary Cancer
{{Medicine
unknown primary origin