Invasion

Invasion is a term used in pathology reports to describe how cancer cells spread into surrounding tissues. A tumour is considered invasive when cancer cells break through the normal barriers that separate different types of tissue. This is an important difference from non-invasive (in situ) tumours, which are still confined to their original location.

Why is invasion important?

The presence of invasion is important because it helps doctors determine how advanced the cancer is and what treatment may be needed. Invasive cancers are more likely to grow, spread, and affect nearby structures. The type and extent of invasion can also influence staging, prognosis, and whether additional treatments like surgery, radiation, or chemotherapy are recommended.

How do pathologists assess for invasion?

Pathologists examine tumour samples under a microscope to look for signs of invasion. They check whether cancer cells have moved beyond their original location and into nearby tissues. Special tests, such as immunohistochemistry, may be used to highlight tumour cells and confirm invasion in certain cases. The depth and pattern of invasion are also assessed, as some types of invasion may indicate a more aggressive cancer.

Types of invasion

Pathology reports may describe different types of invasion, depending on where and how the tumour is spreading.

Common types include:

• Tumour invasion: This refers to the spread of cancer cells beyond the normal tissue boundaries where they first started. For example, a tumour that begins in the lining of an organ may invade into deeper layers of tissue.
• Capsular invasion: Some organs and tumours are surrounded by a capsule, a thin protective layer of tissue. Capsular invasion means the tumour has broken through this barrier, which may increase the risk of further spread.
• Perineural invasion: This occurs when cancer cells spread into the nerves. Tumours with perineural invasion may cause pain, numbness, or changes in sensation, depending on the affected area.
• Lymphovascular invasion: This means cancer cells have entered small blood vessels or lymphatic channels, which are pathways that can carry cancer to other parts of the body. The presence of lymphovascular invasion may increase the risk of cancer spreading to lymph nodes or distant organs.