Cancer of unknown primary

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Types of cancer of unknown primary

Cancer of unknown primary (CUP) means that cancer has already spread to other parts of the body, but doctors don’t know where it started (called the primary site).

Your healthcare team will take a sample of the tumour. The pathologist looks at the sample under a microscope to try to identify the type of cancer cell. The pathology report will also give your doctor information about how much the cancer cells look and act like normal cells. This is called differentiation. Differentiation is an important part of describing and identifying cancer of unknown primary.

DifferentiationDescription

well differentiated

The cancer cells look and act much like normal cells.

The cancer cells are slow growing and less likely to spread than cancer cells with higher grades.

moderately differentiated

The cancer cells don’t look and act exactly like normal cells.

The cancer cells are growing more quickly than well differentiated cancer cells.

poorly differentiated

The cancer cells don’t look and act like normal cells.

The cancer cells tend to grow quickly and are more likely to spread than well or moderately differentiated cancer cells.

undifferentiated

The cancer cells don’t look or act at all like normal cells.

The cancer cells tend to grow very quickly and are most likely to spread to other parts of the body.

Carcinomas

Most cancers of unknown primary are carcinomas. Carcinoma is a type of cancer that starts in epithelial tissues. These tissues are a layer of cells that lines the body’s hollow organs and glands and makes up the outer layer of the skin. CUP is usually one of the following types of carcinoma.

Adenocarcinoma

Adenocarcinoma is the most common type of CUP. Adenocarcinoma is a type of cancer that starts in gland cells that make up the inner lining of some organs.

Adenocarcinoma of unknown primary is more common in elderly people. It is most often found in several places at the same time. The most common places it is found are the liver, lungs, lymph nodes or bones.

Most adenocarcinomas of unknown primary are well-differentiated or moderately differentiated tumours, but some are poorly differentiated or undifferentiated.

Poorly differentiated carcinoma

Poorly differentiated carcinoma is the second most common type of CUP. The cells are very abnormal. The pathologist believes it is a carcinoma but cannot tell what type of carcinoma it is. These tumours are most often found in younger people. Even though these tumours grow quickly, they may respond well to treatment.

Squamous cell carcinoma

Squamous cells are a type of epithelial cell. They are thin and flat and look like a fish scale. They are found in the epithelium that makes up the surface of the skin. They are also in the epithelium lining of other organs, such as the mouth, pharynx, esophagus, anus, cervix and vagina.

Squamous cell carcinoma of unknown primary is most often found in lymph nodes in the neck (called the cervical lymph nodes). The primary site may be somewhere in the head or neck (such as the mouth, throat or larynx) or in a lung.

Squamous cell carcinoma of unknown primary can also be found in lymph nodes in the groin (called the inguinal lymph nodes). The primary site may be in the anus, bladder, cervix, vaginal, vulva or penis.

Neuroendocrine carcinoma

Neuroendocrine carcinomas are different types of tumours that start in the neuroendocrine system. They are very rare. Only a very small number of CUPs are neuroendocrine carcinomas.

Experts think that many neuroendocrine carcinomas of unknown primary start in the pancreas.

Small cell carcinoma is a very aggressive type of neuroendocrine carcinoma that spreads quickly. Most small cell carcinomas of unknown primary are thought to start in the lung. These tumours are often found in many different parts of the body at diagnosis, but they respond well to chemotherapy.

Undifferentiated tumours

If the pathologist tests the tumour but can’t identify it as any particular type of cancer, it is called an undifferentiated tumour, or neoplasm. Undifferentiated tumours are usually very aggressive tumours.

neuroendocrine system

A network of cells throughout the body that have a structure similar to neurons (nerve cells) and produce hormones like endocrine cells. Neuroendocrine cells receive messages (electrical or chemical signals) from the nervous system and produce hormones in response.

The neuroendocrine system is made up of the diffuse neuroendocrine system (neuroendocrine cells and organs in different areas of the body) and the endocrine system (the pituitary, pineal, parathyroid and adrenal glands, thyroid, pancreatic islet cells and the ovaries or testicles).

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