Unknown primary

Unknown Primary Cancer

What is Cancer?

Cancer refers to a group of over 100 diseases where healthy cells undergo changes, grow uncontrollably, and form tumors. Tumors can be either:

• Malignant: Cancerous and capable of spreading to other parts of the body.

• Benign: Non-cancerous and do not spread to other areas.

Typically, cancer is diagnosed by identifying the primary site, where the cancer originated, and determining the secondary sites to which it has spread. Regardless of where it spreads, the cancer retains the name of its primary site. For example, cancer that starts in the breast and spreads to the brain will still be called breast cancer.

What is Unknown Primary Cancer?

In some cases, 2% of all cancers, doctors are unable to identify the primary site even though they can detect cancer in other locations. This condition is called Cancer of Unknown Primary (CUP).

The reasons for failing to identify the primary source can include:

• The primary tumor is too small to detect.

• The immune system has reduced or eliminated the primary tumor.

• Previous surgeries may have removed the primary tumor unknowingly.

Even without identifying the primary site, advanced molecular and pathological tests can predict the type of cells involved in the cancer.

Statistics

In the United States, approximately 32,590 new cases of unknown primary cancer are detected annually.

Risk Factors

The same risk factors that apply to most cancers also apply to cancers of unknown primary origin. These include:

• Age

• Tobacco use

• Sun exposure

• Radiation exposure

• Exposure to chemicals

• Poor nutrition

• Lack of exercise

• Family history of cancer

Symptoms

Symptoms vary depending on the affected organ and the extent of cancer spread. Common symptoms across all cancers include:

• Persistent pain in any part of the body

• Loss of appetite

• Unexplained weight loss

• Chronic cough

• Swelling or lumps in the body

• Changes in urination or bowel movements

• Abnormal bleeding or discharge

• Recurrent fever

Diagnosis

1. Biopsy:

• A tissue sample is taken from the affected area and examined under a microscope using immunohistochemical (IHC) stains to determine the cancer cell type.

• If the biopsy is inconclusive, a molecular cancer classifier assay may be used to identify the cancer’s origin through gene expression profiling.

2. Physical Examination:

• The doctor checks for lumps or abnormalities.

3. Blood and Urine Tests:

• To detect signs of cancer or abnormal function in specific organs.

4. Imaging Tests:

• X-rays, CT scans, MRI, PET-CT scans, and endoscopy help identify the affected areas and determine the spread.

5. Special Tests:

• PSA Test: For prostate cancer in men.

• Mammography: For breast cancer in women.

Types of  Primary Cancer

1. Adenocarcinoma (70% cases):

• Originates in glandular cells found in many internal organs. Determining the exact source can be difficult since adenocarcinomas look similar under a microscope.

• IHC stains and molecular assays may help identify the origin.

2. Poorly Differentiated Carcinoma (20-25% cases):

• Cancer cells are underdeveloped, making it challenging to determine the primary site.

3. Squamous Cell Carcinoma (5% cases):

• Often found in neck lymph nodes, suggesting the primary site may be in the head or neck.

4. Neuroendocrine Carcinoma (1-5% cases):

• Arises from hormone-producing cells, making it rare and difficult to identify.

Treatment

Since unknown primary cancer is metastatic (spreading), localized treatments like surgery or radiation may not be effective. Chemotherapy is commonly used for treatment.

Follow-Up Care

After completing treatment, regular follow-ups are essential to monitor for recurrence and manage any side effects. Follow-up care includes:

• Physical examinations

• Blood tests

• Imaging tests

Unknown primary cancer presents unique challenges because the primary source remains unidentified. Despite this, advanced diagnostic methods and treatments like chemotherapy can help control the disease. Regular follow-ups are crucial to ensure early detection of any recurrence and to maintain quality of life.

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