Tumour infiltrating lymphocytes

Tumour-infiltrating lymphocytes (TILs) are special immune cells that have moved from the bloodstream directly into a tumour. They are part of your body’s natural immune response, which aims to identify and attack cancer cells. Some cancer treatments, known as immune checkpoint inhibitors (such as PD-L1 inhibitors), work by helping these immune cells function better, preventing cancer cells from blocking their natural cancer-fighting ability.

Why are tumour-infiltrating lymphocytes important?

Tumour-infiltrating lymphocytes are important for several reasons:

• Indicator of immune response: When TILs are found in a tumour, it usually means your immune system recognizes the cancer as harmful and is actively trying to fight it. This immune activity is often a positive sign for your prognosis.

• Prognostic value: Higher numbers of TILs are generally associated with better outcomes and longer survival in many types of cancer. Their presence indicates that the immune system is effectively responding to the tumour, suggesting that the cancer might be easier to manage or treat successfully.

• Predicting response to immunotherapy: The amount and activity of TILs can help predict whether you’ll respond well to specific immunotherapy treatments. Tumours with many TILs often respond better to therapies designed to boost your immune system’s ability to target cancer cells.

• Role in specialized cancer treatments: In some cases, TILs can be removed from your body, grown and strengthened in a laboratory, and then returned to your body as a specialized immunotherapy known as adoptive cell transfer therapy. This type of therapy has shown promising results, particularly in melanoma treatment.

In which types of cancer are tumour-infiltrating lymphocytes important?

TILs are found in many types of cancers. Their presence is especially significant in these cancers:

• Melanoma: High levels of TILs in melanoma are linked to better survival rates and improved responses to immunotherapy treatments.

• Breast cancer: Especially in triple-negative and HER2-positive breast cancers, higher numbers of TILs indicate a better prognosis and improved responses to chemotherapy and immunotherapy.

• Lung cancer: In non-small cell lung cancer (NSCLC), increased TILs correlate with improved outcomes and can predict how well patients respond to immune checkpoint inhibitors.

• Ovarian cancer: The presence of TILs in ovarian cancer is associated with better survival rates, indicating an effective immune response against the cancer.

• Colorectal cancer: TILs are especially important in colorectal cancers with a subtype called microsatellite instability-high (MSI-H), where high levels of TILs are linked to better outcomes and positive responses to immunotherapy.

• Head and neck cancers: Higher numbers of TILs in these cancers are associated with improved survival and better treatment responses.

• Bladder cancer: Patients with advanced bladder cancer often benefit from immunotherapy when their tumours contain higher levels of TILs.

How do pathologists identify tumour-infiltrating lymphocytes?

Pathologists identify TILs by carefully examining tumour tissue samples under a microscope, usually obtained through biopsies or surgery. They specifically look for immune cells that have moved into the tumour tissue from the bloodstream. Evaluating the number and activity of TILs helps pathologists and oncologists understand how actively your immune system responds to the cancer.

Questions to ask your doctor

If your pathology report mentions tumour infiltrating lymphocytes, you might want to ask:

• Does my tumour have high levels of TILs?

• What does the presence of TILs mean for my prognosis?

• How do TILs affect my treatment options, especially immunotherapy?

• Could I benefit from therapies designed to enhance TIL activity?

Understanding the role of tumour-infiltrating lymphocytes can help you actively participate in discussions about your cancer treatment and care.