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Types of Cancer of Unknown Primary

Doctors commonly classify cancer of unknown primary (CUP) into one of five major groups after first looking at the cancer cells under a microscope. After more rigorous testing, many of these tumors can be classified more accurately.


Adenocarcinoma accounts for over 60% of tumors classified as cancer of uncertain origin. These tumors are made up of gland-forming epithelial cells. Because glands are involved in secreting or transporting chemicals, adenocarcinoma can form in almost any organ in the body.

The lining of most internal organs is made up of glandular epithelial cells. This can make determining the primary tumor site difficult. The lungs, pancreas, breasts, prostate, stomach, liver, and colon are all common primary sites for adenocarcinoma.

Cancer of Unknown Primary

Poorly Differentiated Carcinoma

Poorly differentiated cancer cells are found in 20 to 30 percent of all malignancies of uncertain origin. These malignancies don’t seem like normal cells and are frequently more aggressive than other types of cancer.

These cancers may have started in lymphocytes, skin cells, neuroendocrine cells (which produce hormones into the blood), or other specialized cells, according to specialized tests. Many weakly differentiated cancer cells, on the other hand, appear so unlike normal cells that clinicians are unable to establish their original cell type.

Poorly differentiated malignant neoplasm

These are unmistakably malignancies, but the cells are so aberrant that the doctor has no idea where they came from. The majority of them are lymphomas, sarcomas, or melanomas. Further examination reveals that several of them are carcinomas.

Cancer of Unknown Primary

Squamous Cell Carcinoma

Squamous cell carcinoma makes up fewer than 10% of malignancies with no known cause. It’s made up of flat epithelial cells that can be found on the skin’s surface or in the lining of specific organs including the mouth and esophagus. Squamous cell carcinoma is a kind of lung cancer.

Neuroendocrine Carcinoma

Diffuse neuroendocrine system cells are the source of these uncommon malignancies. In some aspects, these cells resemble nerve cells, but in others, they resemble hormone-producing endocrine cells. Unlike the adrenal and thyroid glands, these cells do not form a real organ. Instead, they’re strewn over the esophagus, stomach, pancreas, intestines, and lungs, among other organs. Only a small percentage of cancer of unknown primary cases are caused by these tumors. (Further testing reveals that some poorly differentiated tumors are neuroendocrine carcinomas.)

Cancer of Unknown Primary

Doctors do their utmost to classify the sort of cancer, even if they don’t know where it started. This can assist them in deciding on the best treatment option. Because some tumors respond well to specific treatments, it’s critical to categorize the malignancy as thoroughly as possible. This is best accomplished by examining the malignancy under a microscope and performing laboratory testing.


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