Primary cutaneous follicle centre lymphoma

by Jason Wasserman MD PhD FRCPC
October 28, 2024


Primary cutaneous follicle centre lymphoma is an immune system cancer that starts in the skin. It develops from B cells, a type of white blood cell that helps the immune system fight infections. Unlike other lymphomas that affect lymph nodes or internal organs, this type of cancer remains confined to the skin at the time of diagnosis.

What are the symptoms of primary cutaneous follicle centre lymphoma?

Primary cutaneous follicle centre lymphoma usually presents as painless lumps or plaques on the head, neck, or upper body, though it can appear elsewhere on the skin. The lesions are typically red or pink, slow-growing, and do not cause itching or discomfort.

Because these lesions may look similar to other skin conditions, the disease can sometimes go unnoticed at first. Over time, the lumps may grow thicker or more prominent, but they usually remain painless and localized.

What causes primary cutaneous follicle centre lymphoma?

The exact cause of primary cutaneous follicle centre lymphoma is not known. It is not contagious and does not spread from person to person. Researchers believe that genetic changes within B cells may trigger the disease. Environmental factors and immune-related issues might also contribute, but no specific cause has been identified.

How is this diagnosis made?

Primary cutaneous follicle centre lymphoma is diagnosed with a skin biopsy, where a small sample of the affected skin is examined under a microscope. Pathologists look for abnormal B cells arranged in large groups to confirm the diagnosis and distinguish the disease from other skin conditions or lymphomas.

Pathologists also use immunohistochemistry, a specialized test that identifies proteins on the surface of the cancer cells, to confirm the diagnosis. Additional tests, such as imaging scans or blood tests, may be performed to verify that the disease is limited to the skin and has not spread.

What are the microscopic features of primary cutaneous follicle centre lymphoma?

Primary cutaneous follicle centre lymphoma shows different patterns under the microscope:

  • Follicular growth pattern: The cancer cells form clusters, called follicles, that extend through the skin and sometimes into the fat beneath. These follicles lack the structure of healthy follicles, including macrophages and a well-defined mantle zone. The cancerous cells within these follicles multiply quickly and are positive for BCL6, a marker of follicle centre cells.
  • Diffuse growth pattern: In this pattern, the cancer cells spread evenly throughout the skin without forming clusters. Large lymphocytes, called centrocytes, are often present and may have irregular or lobed nuclei. In some cases, the centrocytes are spindle-shaped (elongated). Large abnormal cells called centroblasts may also be found.
  • Reactive cells and stromal tissue: In many cases, non-cancerous T cells mix with cancerous B cells. The cancer cells may also be surrounded by fibrosis (scar), making the disease more difficult to diagnose.
Primary cutaneous follicle centre lymphoma. In this image the tumour is seen in the dermis and subcutaneous adipose tissue (fat).
Primary cutaneous follicle centre lymphoma. This image shows the tumour in the dermis and subcutaneous adipose tissue (fat).

Immunohistochemistry

Immunohistochemistry is used to identify proteins on the surface of the cancer cells, helping confirm the diagnosis.

The following markers are often assessed:

  • CD20 and CD79a: These proteins confirm that the cancer cells are B cells. However, the cancerous cells are usually immunoglobulin-negative, meaning they do not produce antibodies.
  • BCL6: This marker is always positive, showing that the cancer originated from follicle centre B cells.
  • CD10: This marker is often positive in follicular patterns but is usually negative in diffuse patterns.
  • CD21 and CD35: These proteins highlight follicular dendritic cells. In primary cutaneous follicle centre lymphoma, the dendritic cells may form a disrupted network in the abnormal follicles or be absent in diffuse cases.
  • BCL2: Most cases do not show strong BCL2 staining, although faint staining may occur.
  • MUM1 and FOXP1: These markers are typically negative, helping distinguish primary cutaneous follicle centre lymphoma from other lymphomas.
  • CD5 and CD43: These markers are always negative, confirming the diagnosis.
  • Ki-67: The Ki-67 index, which measures how quickly the cancer cells divide, is often high in cases with a diffuse pattern.

How is primary cutaneous follicle centre lymphoma staged?

The pathologic staging of primary cutaneous follicle centre lymphoma describes how far the cancer has spread in the skin and whether the cells have spread to lymph nodes or other parts of the body. This staging system guides doctors in planning the most effective treatment.

T stage: Skin involvement

  • T1: A single lesion is present.
    • T1a: The lesion is smaller than 5 cm across.
    • T1b: The lesion is larger than 5 cm across.
  • T2: Multiple lesions are found in one area or two connected areas of the body.
    • T2a: The lesions fit within a 15-cm circle.
    • T2b: The lesions fit within a 15 to 30-cm circle.
    • T2c: The lesions fit within a circle larger than 30 cm.
  • T3: The lesions are widespread across the body.
    • T3a: Two non-connected areas of the body are involved.
    • T3b: Three or more body areas are involved.

N stage: Lymph node involvement

  • N0: No lymph node involvement.
  • N1: One lymph node group that drains an affected skin area is involved.
  • N2: Two or more lymph node groups or lymph nodes not draining the affected area are involved.
  • N3: The cancer has spread to central lymph nodes (such as those deep within the body).

This staging system helps doctors assess the extent of the disease and select the most appropriate treatment. Local therapies like radiation may be sufficient for early-stage cases, while advanced stages may require more intensive treatments.

What is the prognosis for primary cutaneous follicle centre lymphoma?

Primary cutaneous follicle centre lymphoma has an excellent prognosis, with more than 95% of patients living at least five years after diagnosis. Although the cells may look aggressive under the microscope, the disease usually progresses slowly.

  • Localized disease: Local radiation therapy is highly effective and preferred for patients with only a few lesions. Many patients achieve long-term remission.
  • Relapses: Around 30% of patients experience relapses, with new lesions appearing on the skin. However, these relapses usually do not indicate that the disease is becoming more severe.
  • Systemic treatment: This is only required if the disease becomes widespread, the lesions are unusually thick, or the lymphoma spreads beyond the skin.

Primary cutaneous follicle centre lymphoma that develops on the leg may have a slightly worse prognosis, but it still responds well to treatment. Regular follow-up care is essential to monitor for any changes and ensure the best outcome.

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