If you have been diagnosed with cancer, your pathology report contains important information that will help your doctors better understand your disease, predict its behavior in the future, and plan your treatment.
This article describes the most important pathological features in a cancer report. These pathological features provide the basis for treatment planning in most hospitals.
Cancer is not a single disease. In fact, there are hundreds of different types of cancer that can arise in almost any part of the body. Histology describes the way individual cells, groups of cells, or entire tissues look under the microscope. Pathologists can use the histologic features of a tumour to determine the type of tumour, the site of origin, and the potential behavior of the cancer cells.
For example, some histologic types, such as squamous cell carcinoma, can arise anywhere in the body where there are squamous cells and tend to look similar in most sites. Others, such as adenocarcinoma, arise throughout the body but look different in each site.
By examining your tissue under a microscope and knowing the site of your body involved, your pathologist can assign a name to the tumour, describe its components, and distinguish it from tumours arising in other parts of the body.
The specific cancer type is an important feature because some tumours follow a very slow course and are easily curable while others are aggressive and difficult to cure. Importantly, the histologic type will also help your doctors determine the type of treatment you will require. Occasionally the cancer type cannot be determined accurately and your pathologist will provide a more general name to help guide your care.
Tumour grade is a description of how the cancer cells look under a microscope compared to normal cells. Cancer cells that closely resemble normal cells are said to be ‘low-grade’ or ‘well differentiated’. Cancer cells that look very different from normal cells are said to be ‘high-grade’ or ‘poorly differentiated’. Cells that are so different from the cells that are normally present in the tissue from which the tumour arises that they could not be recognized if examined in isolation are called ‘anaplastic’ or ‘undifferentiated‘.
For some tumour types, specific features (such as necrosis, mitotic activity, and prominent nucleoli) are used to help grade the tumour and the final grade is given a number instead of a name (with the higher numbers representing a higher grade tumour).
Tumour grade is an important indicator because high grade tumours tend to grow faster and are more likely to spread to other areas of the body compared to low grade tumours. Some types of tumours demonstrate very little variability in either appearance or behavior and, as a result, are not given a grade.
Any tissue that needs to be cut by a surgeon in order to remove a tumour from the body is called a margin. When a surgery is performed to remove a tumour, the surgeon usually attempts to remove the entire tumour plus a small rim of ‘normal’ tissue around it. In this type of case, the margin is the normal tissue.
The purpose of a margin is to ensure that no tumour is left in your body. However, for some types of tumours, it is difficult for the surgeon to tell where the tumour ends and normal tissue begins. In these situations the margin may be very small. By examining the margin tissue under a microscope, your pathologist can see how far the tumour cells are from the edge of the cut tissue.
If tumour cells are seen at the edge the margin is said to be ‘positive’. If the tumour cells are away from the cut edge tissue, the margin is set to be ‘negative’. The actual distance that the tumour cells are allowed to be from the cut edge depends on the type of tumour and you should read more about your specific diagnosis for more details. Patients with a positive margin may be offered additional medical management, for example surgery or radiation to the site.
All tissues contain different types of channels that help bring in nutrients and remove waste products. Some channels contain blood and are called blood vessels while others contain a fluid called lymph and are called lymphatics.
Cancer cells can use these channels to escape the main tumour and spread to other areas of the body – a process called metastasis.
When examining your tissue under the microscope, your pathologist will closely examine both the blood vessels and the lymphatics to see if any of them contain cancer cells. When cancer cells are seen within a blood vessel or a lymphatic, the tumour is said to be positive for lymphovascular invasion.
Nerves are bundles of fibres that transfer information between the body and the nervous system (the brain and spinal cord). In contrast to most normal cells, tumour cells are capable of movement and use nerve fibers as a road to travel from the tumour to distant parts of the body. This process is called perineural invasion (because the tumour cells ‘invade’ the space around the nerve).
Perineural invasion can only be seen under a microscope and your pathologist will usually comment on the presence or absence of perineural invasion in your pathology report. Because the tumour cells use nerves to ‘escape’ the tumour, perineural invasion is frequently associated with new tumour growth after the primary tumour has been removed. Perineural invasion can occasionally be seen with benign tumours although it is rare.