Why a Biopsy Is Recommended
Imaging can identify a mass or lesion. Blood tests can indicate that something is abnormal. But there is only one way to know with certainty what a lump or growth actually is at a cellular level, and that is a biopsy. A biopsy is the collection of tissue from the body for examination under a microscope by a veterinary pathologist. It is the definitive diagnostic step that separates guesswork from diagnosis.
Vets recommend biopsies for lumps under the skin, masses found in organs on ultrasound, unusual skin lesions that have not resolved, and abnormal tissue identified during other procedures. The results guide every subsequent decision: whether treatment is needed, what type of treatment is appropriate, and what the likely outcome is.
Fine Needle Aspirate: The Starting Point
A fine needle aspirate, often called an FNA, is not technically a biopsy in the strictest sense — it collects individual cells rather than a tissue sample — but it is usually the first step in evaluating a lump. A small needle is inserted into the mass and cells are aspirated into the syringe. The sample is spread onto a glass slide, stained, and examined under a microscope.
FNA is minimally invasive and can often be done in a conscious patient with no sedation. Results can sometimes be available within minutes if a cytologist is on site, or within a few days if sent to an external laboratory. The limitation of FNA is that it does not always provide enough information. Some tumour types do not exfoliate cells well, meaning the aspirate comes back non-diagnostic. In these cases, a formal biopsy is the next step.
Core Needle Biopsy
A core needle biopsy uses a larger, spring-loaded needle to remove a small core of tissue rather than just cells. This preserves the architecture of the tissue, which matters because some diagnoses rely on seeing how cells are arranged relative to each other, not just what the individual cells look like.
Core needle biopsies are usually performed under sedation or local anaesthesia and can be done as a day procedure. For deep masses, they are often performed under ultrasound guidance so the vet can direct the needle precisely into the target tissue and avoid surrounding structures. They carry a slightly higher risk of bleeding than FNA but remain a low-risk procedure in most cases.
Incisional and Excisional Biopsy
An incisional biopsy involves surgically removing a portion of a mass. This is used when a needle biopsy has failed to provide a diagnosis or when the lesion is in a location where needle sampling is not practical. A small wedge of tissue is taken under general anaesthesia, the wound is closed, and the sample is sent to pathology.
An excisional biopsy goes a step further: the entire mass is removed surgically and the whole specimen is sent for analysis. This serves a dual purpose — it is both diagnostic and potentially curative if the mass turns out to be benign or if clean margins are achieved around a malignant tumour.
The choice between incisional and excisional biopsy is made carefully. For some tumour types, an incisional biopsy first is preferred because knowing the diagnosis before attempting removal allows the surgeon to plan appropriate margins and the owner to make a fully informed decision about proceeding with major surgery.
Recovery After a Biopsy
Recovery depends significantly on how the biopsy was obtained. An FNA requires no recovery time at all. A core needle biopsy may leave a small amount of bruising and local discomfort for a day or two, and most dogs are back to normal activity within twenty-four hours.
Recovery from surgical biopsy follows the same principles as recovery from any soft tissue surgery. The wound should be kept clean and dry. An Elizabethan collar or recovery suit prevents your dog from interfering with the site. Activity should be restricted to lead walks only until the wound has healed and sutures are removed, typically around ten to fourteen days post-procedure.
Watch for signs of infection at the biopsy site: increasing redness, swelling, discharge, or heat. A small amount of bruising in the immediate post-operative period is not unusual. If your dog seems to be in significant pain or you notice anything that concerns you, contact your vet promptly.
How Long Results Take
One of the most anxious parts of the biopsy process is waiting. Histopathology — the examination of tissue sections — takes time. Samples need to be fixed in formalin, processed, embedded in wax, sliced very thinly, stained, and examined by a specialist pathologist. Most external laboratory results in the UK come back within five to seven working days, though urgent cases can sometimes be expedited.
Additional tests may extend this timeline. If the pathologist wants to run immunohistochemistry — which uses specific antibodies to stain for markers that help classify a tumour — a further few days may be needed. Your vet will keep you updated as results arrive.
Understanding the Pathology Report
The pathology report will typically include the diagnosis, a description of the tissue findings, and, in the case of malignant tumours, a grade. Tumour grading describes how abnormal the cells look and how likely the tumour is to behave aggressively. Low-grade tumours tend to grow more slowly and are less likely to spread. High-grade tumours are more aggressive.
Crucially, for surgical specimens, the report will comment on margins — whether the edges of the removed tissue show normal cells or tumour cells. Clear margins mean the tumour appears to have been fully removed. Dirty or incomplete margins may mean further surgery or adjunctive treatment such as radiation therapy is needed.
- Benign: the mass is not cancerous and is unlikely to spread or cause significant harm
- Malignant: the mass is cancerous and carries a risk of local invasion or spread to other sites
- Grade: an indicator of aggressiveness based on cellular appearance
- Margins: whether the edges of the removed sample contain tumour cells or healthy tissue
A biopsy result is not the end of a conversation — it is the beginning of a properly informed one. With a confirmed diagnosis in hand, you and your vet can discuss realistic treatment options, expected outcomes, and the best path forward for your dog's quality of life.