Carcinoma of unknown primary

Carcinoma of unknown primary (CUP) or occult primary tumor is a condition where malignant (cancer) cells are present in the body, but the place of origin(primary site) is unknown. Sometimes the cancer spread is detectable, but the place of cancer origin(known as primary site) is difficult to confirm.

Types of Carcinoma of unknown primary


carcinoma of unknown primary

It starts in the gland cells. At least 60% of CUP are adenocarcinomas. The lymph nodes, liver, lung, and bones are the most commonly affected organs. 

Squamous cell carcinoma

These flat cells are present in the skin and the lining of other body parts such as the nose, throat, lungs, and cervix. Around 5% of CUPs are squamous cell tumors. 

Neuroendocrine tumors

It starts in the small bowel or other parts of the digestive system. But also occur in the lung, pancreas, kidney, ovary, or testicles.

Poorly differentiated carcinoma

It starts in epithelial cells. Around 30% of CUPs are poorly differentiated carcinoma.

Poorly differentiated neoplasm

The tumor cells look so abnormal that it is impossible to identify the origin of cancer. About 5% of CUPs are Poorly differentiated neoplasm. 

Signs and symptoms

Diagnostic tests for carcinoma of unknown primary

Physical exam and health history to check general signs of health, including lumps or anything unusual. A history of the patient’s health habits, past illnesses, and treatments are also essential for diagnosis.

Genetic analysis involves the examination of DNA mutation in a sample of cancer cells. It may help predict the appropriate treatment for carcinoma of unknown primary.

Histologic study includes adding stains to a sample of cancer cells. It is observed under a microscope for specific changes in the cells. 

Immunohistochemistry uses antibodies to check for specific antigens (markers). The test is helpful to help diagnose cancer and type of cancer.

A biopsy removes cells or tissues to view under a microscope. The pathologist checks the tissue under a microscope to look for cancer cells and the type of cancer. 

Light and electron microscopy uses regular and high-power microscopes to look for specific changes in the cells.

CT scan takes detailed images of body areas from different sections like axial, coronal and sagital planes.

MRI scan is a non ionising radiation scan which produces a series of pictures using different sequences like T1, T2 etc.

PET scan (positron emission tomography scan) helps to find malignant tumor cells using radioactive glucose. The malignant tumor cells appear brighter because they are more active and consume more glucose than normal cells.

A mammogram helps detect abnormalities in the breast. It is an x-ray of the breast. 

Endoscopy looks at organs and tissues to check for abnormal areas. It is a thin, tube-like instrument with a light and a camera for viewing.

The tumor marker test detects the presence of certain substances in blood, urine, or tissue released by organs, tissues, or tumor cells. For example, certain substances (CA-125, alpha-fetoprotein) are linked to specific types of cancer when found at high levels.

How to determine the severity?

It is challenging to know the start point of primary cancer. So, doctors can’t accurately stage such cancers.
Still, there are specific tests to find out the location of cancer. Your doctor gathers all the information to help decide on your best treatment options. The scans and tests can suggest the most likely place cancer started.

Treatment options


It is a standard treatment for CUP that has not spread to the other body parts. A doctor may remove cancer and some of the healthy tissue around it. Sometimes chemotherapy or radiation therapy are beneficial after surgery to kill the remaining cancer cells.

Radiation therapy

It uses high-energy x-rays or other radiation to eliminate cancer cells or stop their growth. It is helpful before or after the surgery.


Chemo drugs curb cancer cell growth by killing the cells or depriving their division. The mode of administration for Chemotherapy drugs are oral or intravenous (vein) or subcutaneous. 

Hormone therapy

Some hormones can cause certain cancers to grow. Hormone therapy blocks such action to stop cancer cell growth. 

What to expect after treatment?

You may have a fear of cancer recurrence. Visit your doctor periodically after the treatment ends. For the first year, the follow-up visits may be every three months. After the first year, follow-up visits might be every six months and then once a year after five years.

Do not skip follow-up visits. Your doctors will ask you about new symptoms. A physical examination and diagnostic tests may help to check recurrence.

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What are the alternative treatment options?

The viable alternative options may or may not be standard treatment. It includes vitamins, herbs, and diet. Some of these may be useful. A few may be harmful. Discuss other suitable treatment alternatives with the doctor.

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