What is poorly differentiated carcinoma?

Poorly differentiated carcinoma is a type of cancer made up of cells that line the surfaces of organs. Differentiation refers to the degree to which cancer cells resemble normal cells from the tissue in which they originated. When cancer is poorly differentiated, the tumour cells have lost many of the normal structures and features, making it difficult to determine where they originated. Poorly differentiated carcinomas can arise in various body parts and behave more aggressively than well differentiated carcinomas.

Where does poorly differentiated carcinoma start?

Poorly differentiated carcinoma can originate in many parts of the body. It typically starts in epithelial cells, which line the surfaces of organs and tissues, such as the skin, digestive tract, and lungs. Because poorly differentiated cells resemble the normal cells in their original tissue less, it may not always be clear where the tumour began.

What is the prognosis for a person with poorly differentiated carcinoma?

The prognosis, or expected outcome, for poorly differentiated carcinoma depends on several factors, including the location of the tumour, its size, whether it has spread to lymph nodes or other organs, and how it responds to treatment. Generally, because poorly differentiated carcinomas are often more aggressive, they may be more difficult to treat and have a higher risk of spreading. However, each case is unique, and treatments such as surgery, chemotherapy, and radiation therapy can sometimes be highly effective.

Is poorly differentiated carcinoma an aggressive type of cancer?

Yes, poorly differentiated carcinoma is often considered an aggressive type of cancer. Because the tumour cells are less organized and abnormal, they tend to grow and spread more quickly than well differentiated cancers. This rapid growth can make poorly differentiated carcinomas more challenging to treat and control.

What stage is poorly differentiated carcinoma?

Poorly differentiated carcinoma is a diagnosis, not a stage. The cancer’s stage is determined by additional information, including the size and location of the primary tumour and whether the tumour cells have spread to nearby lymph nodes or distant organs. Staging helps doctors understand how advanced the cancer is and guide treatment.

For example:

• Stage I typically means the cancer is small and has not spread beyond the primary site.
• Stage II and Stage III indicate larger tumours or local spread to nearby lymph nodes.
• Stage IV means the cancer has spread to distant organs.

Staging is an important part of cancer treatment planning and helps provide more information about the expected outcome.

How is this diagnosis made?

The diagnosis of poorly differentiated carcinoma is typically made through imaging studies, biopsy, and microscopic examination of the tumour tissue. Imaging tests, such as a CT scan, MRI, or ultrasound, may first be used to locate the tumour and assess its spread.

A biopsy, where a small piece of tissue is taken from the tumour, is essential for confirming the diagnosis. A pathologist examines this sample under a microscope to identify the specific features of poorly differentiated carcinoma, such as disorganized cell structures and large, irregular nuclei. Special tests, such as immunohistochemistry (a technique that uses antibodies to detect specific proteins on tumour cells), may also be used to confirm that the cancer originated from epithelial cells. Immunohistochemistry helps determine the type of carcinoma and, in some cases, provides clues about where the tumour started.

Microscopic features

Under a microscope, poorly differentiated carcinoma appears disorganized. The cells often have large, irregularly shaped nuclei (the central part of the cell that contains DNA) and may lack the normal structures seen in healthy cells. Pathologists look for these features, which indicate that the tumour cells have lost their original characteristics and do not resemble normal cells from the tissue where they started. This helps confirm the diagnosis and assess how the tumour might behave.

What other tests are performed to confirm the diagnosis?

Immunohistochemistry (IHC) is a specialised laboratory technique used to help identify the origin of poorly differentiated carcinomas. This technique uses antibodies that can bind to specific cell markers. Pathologists apply these antibodies to the tumour sample, allowing them to detect specific proteins that might indicate where the cancer started.

To confirm a diagnosis of poorly differentiated carcinoma, the tumour cells should express certain cytokeratins—proteins made by epithelial cells (cells that line the surfaces of organs and tissues). Cytokeratins help confirm that the cancer originated in epithelial tissue. Common cytokeratins tested in poorly differentiated carcinomas include:

• Pancytokeratins: These are a group of cytokeratins found in many types of epithelial cells.
• Cytokeratins AE1/AE3: A combination of cytokeratins commonly present in epithelial cancers.
• Cytokeratin 7 (CK7): Cytokeratin 7 is typically expressed in tumours originating in specific organs, including the lungs, thyroid gland, upper gastrointestinal tract, female reproductive organs, head and neck sites, and skin.
• Cytokeratin 20 (CK20): Cytokeratin 20 is usually expressed in tumours originating in the lower gastrointestinal tract, such as the colon and rectum.
• Cytokeratin 8/18: Cytokeratin 8/18 is typically found in many types of epithelial cells.

These cytokeratin markers help pathologists confirm the tumour’s origin and make an accurate diagnosis, especially when the cancer cells look very different from normal cells.