Diagnosing Cancer in Dogs and Cats with Cytology

It is not possible to recommend treatment and offer a prognosis for a pet with cancer without aDiagnosing Cancer in Dogs and Cats with Cytology specific diagnosis.  cancer in animals is not a single disease process.  It consists of over 100 different types of diseases that can be grouped into several major categories.  The 2 main methods of obtaining a tissue diagnosis of cancer include cytology and histopathology.  Cytology and histology complement each other and reflect a trade off between a less invasive procedure with cytology and the increased amount of information obtained from histology.  This article discusses cytological diagnosis of cancer.  Cytology is a reliable method of obtaining a tissue sample in a minimally invasive way to obtain a diagnosis of cancer.

Cytology and the diagnosis of cancer

Cytology is a relatively simple procedure to perform and can often be done in animalsCancer in Dogs and Cats and Cytology without anesthesia or sedation.  It involves evaluating individual cells without regard to the architectural structure of the tissue.  Results can be obtained more quickly, are less expensive, and less risky than histopathology.  Common sites that are evaluated with cytology include blood, skin or subcutaneous masses, fluids from various sources (e.g. urine, abdominal or thoracic effusions), lymph nodes, and bone marrow.  With widespread use of ultrasound, the ability to evaluate lesions deep inside the body has been greatly enhanced.

Cytology usually involves inserting a needle into a mass or organ (e.g. liver or lymph node) to obtain tissue or into a body cavity (e.g. chest or abdominal cavity) and obtaining fluid that is placed on a slide, stained, and observed under a microscope.  Cytology is used as a screening tool to try and determine if what is being evaluated shows evidence of cancer or not.  If a cytological diagnosis of cancer is suspected, sometimes the specific tumor type can be determined (e.g. mast cell tumors or lymphoma).  Cytology can sometimes determine if a tumor is benign or malignant, but more often histology is necessary to answer that question.

Cytological interpretation and the diagnosis of cancer

The basic steps of evaluating a cytological sample begins with determining if the tissue sample normal, and if not, whether it is cancerous or inflammatory in nature.  The next step is to determine the type of cancer or inflammation present.  If the sample appears cancerous in nature, then an attempt is made to determine what type of cancer it may represent.  The types of cancer present generally fall into 3 main categories: discrete round cell tumor, a tumor of epithelial origin (carcinoma) or a tumor of connective tissue origin (sarcoma).  There are situations where cytology cannot establish a diagnosis of cancer easily.  This is most commonly seen with sarcomas, in which cells do not shed very easily resulting in samples with little to no cells.

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