What’s in the skin mass of your pet?

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How many times have you noticed a skin mass on your pet and it worried you? Have there been times that you have decided just to watch it or have you been so worried that you decided to have your veterinarian look at it? For those who have taken their pet to the veterinarian, were you told to just monitor the skin mass?  Was a biopsy recommended? What are some possible skin masses that you can encounter on your pet and also how can you diagnose them? If you are looking for some answers to these questions, this article may help.

Even though there are several cancerous skin masses you need to be concerned about in your pet, there are several benign ones that your pet can get also. Here are just a few examples of these skin masses.

Lipoma (aka fatty tumors)

These skin masses are common in dogs, but not so much in cats. They tend to occur in older animals over 8 years of age especially large breed dogs such as Labradors and golden retrievers. The specific cause of these are unknown. In most cases they are soft and flabby when palpated. They are usually free and moveable under the skin. Some of them can feel firm especially if they occur near or under muscle.


Papilloma is a fancy term for warts. They are believed to be caused by a virus. Papillomas vary in appearance from white, flat, smooth skin masses, to cauliflower like masses.  These skin masses are often very fragile and often bleed making them at risk for infections.


This is a skin mass that tends affect young dogs typically 2 years old and younger. They are usually solitary, firm, dome shaped masses which are frequently ulcerated. Histiocytoma are fast growing and sometimes are itchy. Sometimes these tumors can go away on their own after 3 months.


These skin masses  can also be common in dogs. They are typically characterized by a raised mass filled with fluid or skin debris. They can cause problems if they rupture, become infected and inflamed. In most cases, surgical removal allows for a permanent cure.


Unfortunately, we can’t talk about the good tumors without mentioning the bad ones. Here are some of the malignant tumors you may have to worry about.

Mast Cell Tumor

These tumors are common in breeds such as Boxers, Boston terriers, English bulldogs, and Labrador retrievers. Even though mast cell tumors can be solitary, they can also come in different shapes and sizes. Because of this, the tumor is often called the “great pretender”. Sometimes it can look as innocent as a bug bite or highly suspicious like any other malignant tumor. Treatment usually involves aggressive surgical removal leaving the patient with a large scar. Follow-up treatment may include chemotherapy and radiation.


These tumors vary in appearance from brown or black plaques to dome shaped nodules and can appear anywhere on the body. They usually grow rapidly and can be ulcerated. Treatment involves surgical removal and melanoma vaccines can sometime help minimize recurrence.

Squamous Cell carcinoma

These are common malignant tumors in cats and dogs. They tend to be solitary and can occur on the body, legs, nose and lips. Their appearance can be cauliflower-like or ulcerated. They can be very aggressive especially when they occur at the toes often causing loss of nails and infection of nailbeds. Treatment involves surgery if possible followed up with chemotherapy to minimize recurrence.



This tumor is another common malignant tumor in cats and dogs. In cats, viruses such as feline leukemia can cause these to develop. In dogs these tumors seem to be more common in females and cocker spaniels seem to be a breed predisposed to this condition. Their appearance is typically irregular and nodular in shape. They tend to have a firm consistency. Fibrosarcomas grow quickly, invading nearby tissue and often spreading to other parts of the body. Because of the nature of the tumor, they may recur despite surgical removal.

Options to consider for diagnosis of the skin mass

If you ever bring your pet to the veterinarian to examine a skin mass, they may discuss with you the following options:

  • FNA (Fine Needle Aspiration). This involves sticking a needle inside the skin mass and attempting to aspirate cells for a diagnosis. The ability to obtain a diagnosis by this method depends on several factors. One is the type of tumor. Some tumors yield a moderate amount of cells with a needle while others don’t. The location of the tumor– If the tumor is located in an area covered in fat or muscle then it may be difficult to get the appropriate cells you need for a diagnosis. Technique- A FNA is generally not a difficult technique to perform but if you have a dog that is resistant to the idea the sample may not be of good quality due to movement.
  • Impression smear– This technique can be performed on masses that are ulcerated. This involves pressing a slide on the ulcerated area and looking to see what type of cells that are picked up. This is probably the least reliable of the techniques because it relies on the mass being ulcerated. Additionally if there is an active infection, you may just get bacteria.
  • Biopsy- This is the most reliable technique for a diagnosis but also the most invasive since it involves surgery. The technique can involve full or partial removal of the skin mass. Information provided by the biopsy can be helpful in not only identifying theskin mass but also in determining a prognosis. Depending on the tumor type, the results can also help determine if the skin mass has spread to other parts of the body or if removal has lead to a cure.


So how do you decide what to do if you find a lump on your pet? While your veterinarian can definitely assist you on what is the best for your pet I thought I would list some guidelines to help with your decision.

If you are at all concerned with any skin mass on your pet trust your gut. If you have any concern, just have it tested by one of those methods above. Having a peace of mind once it is diagnosed may be worth it.

Below is a table that lists general characteristics of benign masses vs malignant masses. Just remember not all skin masses follow these generalizations. So this table should be only used as a guide not as a absolute.

Behavior of Skin Mass Benign Skin Mass Malignant Skin Mass
Growth Rate Grow very slowly Rapid Growth
Growth size and shape limited boundary with growth. Well uniformed shape unlimited boundary, lacks any specified shape or structure.
Damage to skin and underlying tissue minimal to no skin irritation, no involvement of underlying tissue Skin irritation is common with infections, invasion of underlying tissue


Hopefully this information will help you make the best decision for treating your pet’s lump. Thanks for reading!

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