Cancer of Unknown Primary Diagnosis

Cancer of Unknown Primary Diagnosis


For cancers of unknown primary, doctors at Memorial Sloan Kettering use a combination of sophisticated tests to determine the type of cancer and to prepare treatment plans. Treatment is managed by a team of doctors. We work together to ensure that every individual receives personalized care.

First, the tumor tissue from a biopsy or surgery is reviewed by an MSK pathologist. Next, a doctor will review the studies that have already been performed on the individual. Care teams may recommend additional tests to help identify the primary site of disease.

Sometimes, doctors can identify a likely primary site based on certain features in a tumor and the places in the body where the cancer is present, including in the following scenarios:

For many people, however, the primary site cannot be found. In these cases, the diagnosis focuses on identifying the location of the cancer and the type of cells that make up the tumor to develop a care plan.

For most people with cancer of unknown primary, doctors rely on information from blood tests, imaging studies, molecular analysis, and pathology tests to learn more about a tumor.

Many people with a tumor designated as cancer of unknown primary have already had some of these tests when they come to MSK. Our doctors may do additional laboratory and imaging tests to narrow down the possible organs or parts of the body where the cancer began. Tests may also be needed to identify the kinds of cells in the tumors. With these results, our doctors can recommend the most-effective treatment possible.


Our doctors use state-of-the-art imaging tests to create high-quality pictures of tumors. These images pinpoint the location of a tumor and where else the cancer might be in the body. Diagnostic imaging also provides information on the size and density of a tumor. This helps our doctors determine the most-effective care plan. We may use one or more of the following imaging techniques:

CT Scans

CT uses X-rays to produce an image that reveals the location and size of a tumor or tumors, as well as whether the cancer has spread into the lymph nodes or other areas.


High-frequency sound waves may be used to help map the location and number of tumors in the body. Ultrasound can also help distinguish a cancerous tumor from a noncancerous (benign) growth.


Before imaging with PET, a small amount of radioactive sugar is injected into a vein. Cancer cells absorb sugar more rapidly than normal cells, so this solution helps highlight the cancer cells on a PET scan. PET is often combined with CT to identify areas of the body where cancer of unknown primary has spread, even when the primary site cannot be found.


A biopsy (removal of tumor tissue or fluid for examination under a microscope) is commonly performed to confirm a diagnosis of cancer of unknown primary and to obtain cells for further study under a microscope. A pathologist examines the sample to determine the type of cells involved. Depending on the location of the tumor, doctors may perform one or more of the following types of biopsy:

Core Needle Biopsy

A large needle is inserted into the tumor to obtain tissue for sophisticated pathology tests. Imaging tests may help guide the placement of the needle. Core needle biopsy is usually performed using a local anesthetic.

Fine Needle Aspiration

A smaller needle is inserted during a core needle biopsy to extract a sample of cells or fluid for examination under a microscope. The biopsy can also be used for additional studies in the laboratory.

Surgical Biopsy

In this type of biopsy, a surgeon removes some or all of a tumor or affected lymph nodes. General anesthesia is required if the tumor or lymph node is located in the chest or belly.

Pathology Tests

In many cases, routine laboratory tests do not provide enough information about a cancer of unknown primary to identify or narrow down the possible primary site. Memorial Sloan Kettering’s pathologists are highly experienced in identifying subtle cell patterns that may indicate certain types of cancer.

We use many laboratory tests to find out important information about the tumor type and how it will respond to treatment. These include tests that use antibodies to screen for proteins produced by certain tumors. We may also use such tests as MSK-IMPACT™. This can identify genetic changes that could be targeted with drugs or immunotherapy.

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