Hallmark Cells: Definition

Hallmark cells are a distinctive type of abnormal cell seen under the microscope in a cancer called anaplastic large cell lymphoma (ALCL). These cells are a clue that helps pathologists recognize and diagnose this disease.

What do hallmark cells look like?

Hallmark cells are large and have a very characteristic appearance. Their nuclei, which are the parts of the cell that contain genetic material, are often shaped like a horseshoe or kidney. The nucleus is pushed to the side of the cell, leaving a clear space around it. Because of this unusual shape and position, hallmark cells stand out when examined under the microscope.

Why are hallmark cells important?

Hallmark cells are important because they are a key feature of anaplastic large cell lymphoma. When pathologists see hallmark cells in a biopsy, it strongly suggests the diagnosis of ALCL. However, hallmark cells are usually found alongside other abnormal features, and pathologists use special tests to confirm the diagnosis.

Are hallmark cells cancer?

Yes. Hallmark cells are cancerous T cells. Their unusual shape is the result of genetic and structural changes inside the lymphoma cells. These changes allow the cells to grow uncontrollably and form tumours.

What other tests may be performed?

Although hallmark cells can suggest ALCL, they are not enough on their own for a final diagnosis. Pathologists also perform additional tests, such as:

• Immunohistochemistry, which shows that hallmark cells are strongly positive for a protein called CD30.

• ALK testing, which determines whether the lymphoma is ALK-positive or ALK-negative, two related but different forms of ALCL.

Questions to ask your doctor

• Were hallmark cells seen in my biopsy?

• Does this mean I have anaplastic large cell lymphoma?

• What additional tests were performed to confirm the diagnosis?

• Is my lymphoma ALK-positive or ALK-negative, and what does that mean for me?