Your diagnosis

Follicular lymphoma

This article will help you read and understand your pathology report for follicular lymphoma.

by Philip Berardi, MD PhD FRCPC, updated December 24, 2020

Quick facts:
  • Follicular lymphoma is a cancer that comes from immune cells called lymphocytes.
  • The tumour can start anywhere in the body although the most common locations are lymph nodes, the gastrointestinal tract, skin, and breast.
  • Follicular lymphoma is the second most common type of lymphoma to effect adults.
The immune system

Your immune system is made up of many different kinds of cells and each play an important role protecting your body from infections and helping you heal after an injury. Unlike other types of organs, your immune system is spread throughout your body. Most immune cells are found in small organs called lymph nodes. Lymph nodes are located throughout your body. Large numbers of immune cells can also be found in the blood, skin, gastrointestinal tract, and bones.

What is follicular lymphoma?

Follicular lymphoma is a type of cancer that comes from a special type of immune cell called a lymphocyte. Follicular lymphoma can start anywhere in the body where lymphocytes 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.

Follicular lymphoma is the second most common lymphoma to effect adults.

Patients with lymphoma 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.

How do pathologists make this this diagnosis?

The diagnosis of follicular lymphoma is usually made after a small piece of tissue is removed in a procedure called a biopsy. Depending on the features of the cancer, patients are then typically either followed (‘watch and wait’) or treated by chemotherapy and/or radiation therapy.  Occasionally and only in specific situations is the tumour removed by surgery.


Grade is a word pathologists use to describe how different the cancer cells look compared to normal lymphocytes. Follicular lymphoma is given a grade from 1 through 3. Grade 3 follicular lymphoma can be further subdivided into grade 3A and 3B.

The tumour grade depends on how the cancer cells look when examined under the microscope. Pathologists determine the tumour grade by counting the number of large cancer cells called centroblasts in a given area. Tumours with more large cells are given a higher grade.

Grade 1 and grade 2 tumours are grouped together and are referred to as low-grade or grade 1-2 because they tend to grow and spread very slowly. Tumours that behave in this manner are also referred to as indolent.

Grade 3 tumours are referred to as high-grade because they tend to behave in a more aggressive manner and are associated with a poorer overall outcome.

Over time, low-grade (grade 1 or grade 2) tumours can change into high-grade (grade 3) tumours. If you develop new symptoms and were initially diagnosed with a low-grade follicular lymphoma, your doctor may perform another biopsy to see if the tumour has changed to a higher grade.

Transformation to diffuse large B-cell lymphoma

Over time, some follicular lymphomas will increase in grade (become more aggressive) and the final step in this change is the development of a more serious form of lymphoma called diffuse large B-cell lymphoma.

Pathologists call the development of diffuse large B-cell lymphoma from follicular lymphoma transformation. Your pathologist will carefully examine your tissue for any evidence of diffuse large B-cell lymphoma.

Pattern of growth

Pattern of growth is a term pathologists use to describe the way groups of cancer cells look under the microscope. When the cancer cells are arranged in small round groups the pattern is called follicular. When the cancer cells grow in very large shapeless groups and there is no space between the groups, the pattern is called diffuse.

The diffuse pattern can be associated with a worse prognosis. If a grade 3B tumour shows a diffuse pattern of growth, the diagnosis changes from follicular lymphoma to diffuse large B-cell lymphoma.


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

Immunohistochemistry is commonly performed on cases of follicular lymphoma to confirm the diagnosis and to exclude other diseases that can look similar under the microscope.

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.

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

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