Diagnosis of equine cancer

Tumour classification

Tumours are classified according to their tissue of origin. It is also important to grade tumours so we can predict their behaviour. Again, this is achieved via histopathology.

Implications for horse health

The type of tumour and the anatomical region of the horse it affects will have different implications on the health of the horse. If you suspect cancerous changes in your horse it is important that you contact your vet at the earliest opportunity. The earlier a tumour is diagnosed and treated the easier it is to remove and the greater the chance of a successful outcome.

Types of equine cutaneous (skin) cancer

There are a number of tumour types that affect horses. However, here we address the most common types.

Appearance of tumour and horse signalment

The external appearance, location and growth pattern of a tumour and the breed and age of your horse will give your vet a degree of suspicion as to what type of tumour is present. However, for accurate diagnosis further laboratory tests will normally be required.

Biopsy

This procedure removes a small section of a tumour for examination under a microscope (histopathology). This will allow grading of the tumour and will help with choosing the optimal treatment and establishing a prognosis. Biopsies should be performed on any growth that cannot be diagnosed on appearance, or isn’t responding to medical management. A biopsy is not a form of treatment, and must be followed up with appropriate management of the tumour.

Cytology

This is the microscopic analysis of isolated cells from within a suspected tumour. Cells are usually taken via needle aspiration from a solid growth or from body fluids near a tumour. Cytology is less invasive and quicker to perform, but provides inferior diagnostic and grading information compared to a biopsy, and frustratingly can be often be non-diagnostic.

Treatment of equine cancers

Unfortunately, there are limited numbers of studies conducted in the field of cancer treatment in horses compared to humans and small animals. Therefore, protocols vary and are based on limited research and the experience of the clinician in charge of the case.

Treatment can be grouped into three types:

  1. Ablative- surgical or laser
  2. Cytotoxic- radiation and chemotherapy
  3. Biological- immunotherapy

For many tumour types a combination of treatments maybe employed. An example is surgical reduction of the primary tumour with follow up chemotherapy.