Skin tumors

Guinea pigs can be affected by a variety of skin tumors. Some of these are benign (generally harmless) and some can be malignant (cancerous). It is often not possible to diagnose what type a tumor is by looking at it and further diagnostics are often required to decide upon a diagnosis and treatment plan.

Trichoepitheliomas are one of the most commonly diagnosed skin tumors in guinea pigs. They are usually benign and have a cystic appearance. They can appear anywhere on the body but are more commonly seen on the back and can contain hair and fluid. They may grow to a considerable size and can begin to irritate the guinea pig and ulcerate. For this reason, it is often recommended that they are surgically removed in their entirety.

Abscesses appear as solid masses and can occur anywhere on the body. They contain pus and can appear after a wound becomes infected (such as a fight wound) or due to dental disease. Those forming from fight wounds can be removed surgically. Dental abscesses are often harder to treat due to their location, and long-term treatment may be required.

Mammary tumors occur in older, female guinea pigs and can spread cancer cells to other parts of the body. For this reason, mammary tumors should be removed at the earliest opportunity and x-rays are often taken of the chest to ensure there is no spread. Spaying may also be recommended.

Lipomas are ‘fatty’ lumps and appear anywhere on the body. They are generally harmless and do not need removing unless they are impeding grooming or movement, and can grow to a considerable size.

It is often not possible to diagnose what a tumor/mass is simply by looking at it. Your veterinarian will examine your guinea pig and look and feel the mass/es. They are likely to suggest further diagnostics. A fine needle aspirate (FNA) is when a small needle is inserted into the lump and some of the cells are drawn off and placed onto a microscope slide. The cells can be looked at under a microscope to determine what they are and therefore what the tumor/mass is. Sometimes FNA’s are not diagnostic, especially if the tumor/mass is very deep (and the needle isn’t long enough to get a good sample), if the sample is contaminated with blood (some masses bleed more than others) or if the mass is pocketed and the cells are not throughout the whole tumor.

Biopsies may be required to obtain a diagnosis. This is when a section of the tumor is taken under general anesthetic. It can then be sent away to a laboratory for a diagnosis.

It is not always possible to determine if a tumor is painful or not. This depends on the size, type and location of it. If it is ulcerated, situated in an area under movement or tension, etc, it is likely to be causing discomfort.

Guinea pigs will always try and hide signs of pain, so even if your guinea pig seems well in every other way, if you notice a tumor you must consult your veterinarian as soon as possible.

Your veterinarian will advise you on whether the tumor needs removing or not. Those that are benign and are not painful or inhibiting movement, eating or grooming are often okay to leave to monitor. If the mass is likely cancerous, ulcerated, painful, large and causes the guinea pig problems then it is likely to require surgical removal. This will need to be performed under a general anesthetic which carries some risks, but if surgery is not performed euthanasia will be required either immediately or within a short period of time before the guinea pig starts to suffer.

It is likely that after surgical removal, your veterinarian will suggest histology upon the tumor if they are concerned it may be cancerous, return or have spread to elsewhere in the body. The tumor is sent to an external laboratory that examines slices of it and looks at the cells. They are able to determine the exact type of tumor, if it is cancerous or benign, if it is likely to spread locally or to other parts in the body and if the whole tumor has been removed. Histology normally costs around £100 depending upon which laboratory is used.