How is cancer diagnosed?

How is cancer diagnosed?

Your veterinarian may suspect that your pet has cancer based on certain clinical signs (a lump, loss of appetite and energy, loss of weight). X-rays may be useful in detecting internal tumors, including metastases. Blood tests can help indicate some tumors. In order to identify most tumor types, it is necessary to obtain a sample of the tumor. Depending upon the type of tumor suspected, your veterinarian may obtain this sample through a fine needle aspiration, a punch biopsy, a tissue biopsy or a full excision biopsy. In some cases, an exploratory surgery or ultrasound guidance may be needed.

"In order to identify most tumor types, it is necessary to obtain a sample of the tumor."

The simplest approach in many cases is the aspiration (suction removal) of tumor cells with a syringe and needle. It does not require general anesthesia or surgery. Microscopic examination of the cells obtained is called cytology. A few tumors can be accurately diagnosed with cytology.

However, in most cases a biopsy sample of the tissue must be examined in order to reach an accurate and reliable diagnosis. Your veterinarian will send the sample to a specialized laboratory for examination by a veterinary pathologist. The preparation and microscopic examination of tissue is called histopathology.

The histopathology report typically includes words that indicate whether a tumor is 'benign' (non-spreading, local growth) or 'malignant' (capable of spreading to other body sites). Malignancy is often shown by tumor names ending in "carcinoma" or "sarcoma". These, together with the origin or type of tumor, the grade (degree of resemblance to normal cells) and stage (how far it has spread) indicate how the cancer is likely to behave.


The veterinary usually adds a prognosis (what will probably happen). This may include a prediction about the probability of local recurrence or metastasis (distant spread).