Classic follicular lymphoma

by Jason Wasserman MD PhD FRCPC
September 20, 2023

What is classic follicular lymphoma?

Classic follicular lymphoma (cFL) is a type of immune system cancer that starts from specialized B cells. It is the second most common type of lymphoma to affect adults. cFL is a recent term that encompasses FLs previously classified as grade 1, grade 2, or grade 3A.

What are the symptoms of classic follicular lymphoma?

Patients with cFL may notice a painless lump or swelling that slowly increases in size over time. Other symptoms of follicular lymphoma include fatigue, unintentional weight loss, loss of appetite, night sweats, and fever.

What causes classic follicular lymphoma?

What causes cFL is currently unknown. However, a number of risk factors that may increase the chance of developing cFL have been identified. These risk factors include cigarette smoking, hepatitis C infection, Sjogren’s syndrome, obesity, and having a first-degree relative who was previously diagnosed with follicular lymphoma.

Where in the body is classic follicular lymphoma found?

cFL can start anywhere in the body where B cells gather in large numbers. The most common locations include lymph nodes, the gastrointestinal tract (in particular the stomach and small bowel), the skin, and the breast.

How is the diagnosis of classic follicular lymphoma made?

The diagnosis of FL is usually made after a small piece of tissue is removed in a procedure called a biopsy. The tissue is then sent to a pathologist for examination under the microscope.

What does classic follicular lymphoma look like under the microscope?

Most cFLs are made up of small, dark cells that look similar to normal B cells. However, some tumours contain larger, more abnormal-looking cells. Pathologists use the term pattern of growth to describe the way the cancer cells are arranged. When the tumour cells are arranged in small round groups the pattern is called follicular. When the tumour cells grow in very large shapeless groups and there is no space between the groups, the pattern is called diffuse.

Is classic follicular lymphoma graded?

In the past, follicular lymphoma was divided into four grades: 1, 2, 3A, and 3B. However, recent studies have shown that there is very little difference in long-term outcomes for patients with grade 1, 2, and 3A disease. For this reason, grades 1, 2, and 3A are now grouped together under the term cFL which is itself not graded. What was previously described as grade 3B follicular lymphoma is now called follicular large B cell lymphoma.

What other tests may be performed to confirm the diagnosis of classic follicular lymphoma?

Pathologists often perform immunohistochemistry (IHC) to confirm the diagnosis and exclude other conditions that can look like cFL under the microscope. Another test called flow cytometry may also be performed.

IHC is a special test that allows pathologists to learn more about the types of proteins made by different types of cells. Cells that produce a protein are called positive or reactive. Cells that do not produce a protein are called negative or non-reactive.

Classic follicular lymphoma commonly shows the following immunohistochemistry results:

• CD20 – Positive.
• CD10 – Positive.
• BCL2 – Positive.
• BCL6 – Positive.
• CD23 – Negative.
• CD3 – Negative.
• CD5 – Negative.
• Cyclin D1 – Negative.

What is the Ki-67 labelling index and why is it important?

The Ki-67 labelling index is a way of estimating how quickly cells are dividing. Generally, the quicker the tumour cells divide (the higher the Ki-67 labelling index), the more concerned your doctor will be that your lymphoma will behave aggressively.

What does transformation mean and why is it important for classic follicular lymphoma?

Over time, some cFLs will change to become a more aggressive type of lymphoma called diffuse large B cell lymphoma (DLBCL). This change is called transformation. All tumours are carefully examined for any evidence of transformation and if seen, it will be described in your report.