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Giant cell tumor, more commonly known as malignant fibrous histiocytoma, is a subtype of fibrosarcoma and is usually malignant due to its rapid growth deep within the skin, its octopus-like shape, and the presence of spindle cells, which indicate cancer. Though rare in cats, malignant fibrous histiocytoma is the most common type of soft tissue tumors in cats, making up 60% of all sarcoma diagnoses. In rare cases, it can spread to muscles and to the lymphatic system. There is a high recurrence rate even after surgery.
Giant cell tumors are frequently found in the skin and connective tissues of middle to older aged cats such as at vaccine injection sites between the shoulder blades or in the soft tissue of the hind legs. They can also be found in the neck, abdomen, and forelimbs. There are no indications that giant cell tumors affect one sex more than the other.
All organs in the body have fibrous connective muscle tissue, nerves, and special white blood cells called macrophages or histiocytes. These blood cells work with the immune system to help eliminate harmful waste from the body and defend against disease. When there is an abnormal growth of these cells, benign tumors called histiocytomas may develop.
There are also connective tissue cells called fibroblasts that help the body to heal after injury. If a histiocytoma is found to have fibroblasts fused to it, as well as additional multinucleated cells within the presence of a large amount of collagen, it is called a giant cell tumor and is usually malignant. Its development is often due to the immune system attacking an infectious agent cell.
Tumors under the skin or fat layers may appear in different sizes and shapes, but they are almost always firm and fleshy to the touch. Clusters of lumps can appear in one location. Other symptoms include:
The reason any cancer develops is unknown. Many doctors believe that it may be the result of a series of unfortunate issues that the pet is experiencing, some environmental and some genetic. Therefore, the true cause of malignant fibrous histiocytoma is also unknown. However, there are two strong suspicions of causes:
Recombinant Feline Leukemia Virus
Malignant fibrous histiocytoma may be instigated by feline sarcoma retrovirus (a variety of feline leukemia virus). This theory applies mainly to middle-aged cats but not older, cats since they have developed an immunity to the virus over time. Therefore, if an older cat is found with a tumor, it is highly probable that it is not related to the virus.
Since tumors sometimes develop at injection sites for certain rabies and feline leukemia vaccines, manufacturers are testing to see if their vaccines are a contributing factor. Studies address whether the vaccines can be administered less frequently and if there is a safer location on the body in which to give the vaccine than between the shoulder blades, on the lower neck, or in the leg.
After an initial physical exam, your veterinarian will collect whatever evidence can be found to determine the cause of the lump. Typically, x-rays and ultrasounds are taken to show the location of the lump as well as its size and shape. Additional testing such as a blood test and a urinalysis may be conducted to rule out any underlying conditions. Note that these tests will not give an indication if the lump is cancerous or not.
Because a tumor can have varying characteristics, both between different tumors and even within the same tumor, it is very important to test for its exact type in order to identify what kind of cancer your cat has. For that reason, your veterinarian will conduct either a needle aspiration or a biopsy to make an accurate diagnosis.
Needle aspirations are common, but they are rarely accurate. The only way to make a true determination of the type of cancer is to take a biopsy of the lump and send it to a specialized laboratory for testing. Because of the octopus-like structure of the tumor, in which its “legs” burrow deep into the tissue, exploratory surgery is necessary to obtain a viable sample of the lump. The laboratory will determine if spindle (cancerous) cells are present in the sample. If the entire lump was taken out, the laboratory will determine if all of the cancer cells were removed from the area and that the margins, or the area around the tumor, are clean.
After the laboratory has finished testing, a histopathology report is generated to help the veterinarian determine a course of treatment. The report will show the type of tumor the lump is, what its prognosis is, and what the probability of recurrence will be.
If the tumor is confirmed to be cancer, rapid and aggressive surgical removal of the tumor and the surrounding deep tissue by a board-certified surgeon is necessary to have the best chance of success. If the tumor is located on a limb that is determined to be untreatable, the surgeon may amputate the limb to completely eradicate the cancer.
It is sometimes difficult to determine if the entire tumor has been removed, which means the chance of recurrence is very high. Recurrence usually indicates that the cancer has invaded deeper into the tissues and may be spreading. Additional surgery after recurrence does not necessarily increase your cat’s chance of survival. As a result, your veterinarian may choose to use radiation treatment either before or after surgery to lessen the probability of recurrence. Chemotherapy may also be administered if the tumor is very large, has metastasized, or cannot be removed due to the level of its invasiveness.
Radiation treatment appears to only have an impact if it is given in high doses, which is why chemotherapy is becoming more popular. Although chemotherapy is not often a complete cure, it may add years to your cat’s life and provide a higher quality of life.
After surgery, it is very important for you to keep the incision site clean. A collar may be placed on your cat to prevent it from interfering with its healing.
If you notice any swelling or bleeding around the incision site, or if there are sutures missing, call your veterinarian right away.
Medications to address symptoms related to any underlying conditions will be administered to make your cat more comfortable.
Side effects due to radiation treatment and/or chemotherapy are possible. Conduct ongoing conversations with your veterinarian for the best possible treatment of these effects.
The prognosis of a malignant fibrous histiocytoma tumor will depend on its location and how fast it is growing. Although most do not metastasize, they are usually locally invasive and difficult to fully remove during surgery, which means the probability of recurrence is high. More than 70 percent recur within one year of surgery. If the tumor is determined to be vaccine-associated, the rate of recurrence is 90 percent. The histopathology report generated by the laboratory will give specific expectations of recurrence or metastasis for your cat.
It is important to remember that the overall risk of your cat having malignant fibrous histiocytoma is extremely low. Current estimates are that the risk is from 1:1,000 to 1:10,000 that your cat will have a tumor of this kind. Protecting your cat against disease through the use of vaccines is still highly recommended and far outweighs the risk of cancer.
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1 found helpful
My vet said my cat has fibrous cysts/lumps. He has several. Hes licking the parts that aagainst his skin making them bleed. I cant afford the surgery if hes even able. Is there a way of applying meds to the skin to heal the skin hes licking? I wish i could attach a picture. Or am i prolonging his suffering?
Feb. 28, 2018
If Spooky is licking the lumps too much you should consider placing a cone on him to allow the affected skin to heal and you should also bathe the wounds with a dilute antiseptic; I cannot say whether you should consider putting him down or not as this is your decision to make but you should think about what is in Spooky’s best interests. Regards Dr Callum Turner DVM
Feb. 28, 2018
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0 found helpful
My cat Tomate, has a spindle cell tumor located in his back. Here’s our story: About a year ago I felt for the first time the little lump. As soon as I felt it I took him to the vet and they put him through surgery right away. The doctor who took care of him back then, said the biopsy to the removed lump had shown to be a cancer, but did not explain much more. The only thing he said was “it might come back”. Three months laters I felt the lump back. I waited around three months to take him back to the vet, and the lump grew, twice the size of a grape. In my head, I thought the doctor will just put him through surgery again and get rid of the tumor, but I was naive to believe that. Thai new doctor told me I should bring my cat to an oncologist. We made an appointment with the only oncologist in this area, at the Veterinary cancer group in Culver City CA. The options now were radiation to reduce the size of the tumor before they could remove it with surgery. The treatment takes 4 weeks. We had to bring Tomate to his appointment Monday to Friday for four weeks. They apply a small dose of anesthesia to assure that the cat is completely still while they shoot the radiation to the tumor. The length of the appointment is around an hour and a half. Tomate showed few side effects, during the month of treatment he acted normal and usually was always just excited to get back home after the treatment. The sides effect were a bit visible a week after he ended his 4 week treatment. Just a bit lethargic and lack of appetite. After being done with radiation, the doctor now have us the green light to do surgery... however the conversation with the surgeon is different. She can feel some larger tendrils around the tumor and has recommended a new CT scan, which will show her the current stage of the tumor and its tendrils. She says she does not want to do surgery without getting a CT scan because it might not be worth it if it doesn’t buy us at least a year. It’s is frustrating... I had high hopes that radiation was going to be effective enough to shrink tendrils and reduce tumor size, but the reality is that it’s all a gamble. I maxed my credit cards and currently owe 10k only for the radiation treatment. A new CT scan is $2000 and the cost of surgery won’t be less than $3000. It is a high cost to pay to not have the certainty that my cat will stay with me at least more than a year... I am not saying I regret going through this process, who knows! Maybe the new cat scan will show some hopes and after surgery he will be okay for a while, however as the article above says it... there’s a high chance of recurrence and there’s not a lot of information around about how effective the radiation really is. This is a really crazy expensive treatment and I am just telling the story here so if you have a similar case, you can see what your options are... I know that for me, Tomate is half my life, which is why I’ve decided to put myself in debt just so I could try to extend his life... I guess that’s how we are... immensely attached to life and stretch the existence of the ones we live as much as we can. I will make sure to update this comment in a couple of months, when I can tell you all what happened after surgery. On a side note, there’s more holistic treatment that I have no idea if they work or not but they might be helpful if ur cat is at an early stage. Ozono can supposedly help to make oxygen run through the body and cancer don’t like oxygen. If you have a kitten and u are vaccinating them, make sure they do it on a leg... I think is easier if this tumor show up a on a limb, as it can be amputated and that way getting rid of the cancer might be easier. I wish I’ve known better... I wish I had my cat on insurance, I wish this had never happened... but here we are for a reason. For now Tomate, besides his little lump, looks happy! Eats well and lives running around and playing with his other cat friends... so I guess I’ll continue my fight against the cancer and hoping to keep my cat alive and happy.
Short hair tabby
0 found helpful
My cat had a spindle tumor removed from her tail. 8 weeks later I feel a large growth about an inch from the one she had removed very neat the base of the tail. I made another trip to the vent and it was same type of growth. I decided not to amputated be her tail and there was not enough skin to remove and stitch. Sadly I made the decision to put her to sleep. It broke my heart and find myself second guessing my decision. I do feel that her quality be of life would have declined and most likely the tumors would have reshown there ugly selves someplace else. So as difficult as it is to loose my friend I can say I did it for her and didn't want to put her through the agony of being confined, wear a protective collard and pushing pain meds down her throat. Tough decision to make, Heart broken.
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