Injection Sarcoma in Cats and Dogs

Dog Health

Vaccination is a preventive treatment method used to reduce the severity of future diseases. Many of the vaccines used today can completely prevent diseases. Each treatment method brings with it some risks, but before it is applied, the pros of the treatment and the risks that may occur are compared. The risks of side effects in vaccine administration are generally very low. Side effects that are considered particularly serious are rare. One of the rare but high-risk side effects associated with vaccines is sarcoma, that is, tumor formation at the vaccine site. In this article, you can find answers to frequently asked questions about injection sarcoma.

What Is Injection Sarcoma and Why Does It Happen?

One of the rare but serious side effects of the vaccine is the formation of a tumor in the vaccination area. This condition, called sarcoma, can occur weeks, months or even years after vaccination. It was first observed in the 1990s that aggressive tumors form in the areas where vaccination or injection was made in cats. Initially, the vaccine or injection was thought to cause cancer. However, thanks to the studies that started in 1997, important data were recorded about the tumors formed after the injection.

Soft tissue sarcomas are known to be very difficult to treat in cats, deep-rooted tumors that occur long before vaccination. There are different types of soft tissue sarcomas and fibrosarcoma is one of them. Fibrosarcoma does not usually spread throughout the body like cancer does. Instead, it goes deeper in the region where it is located. Moreover, it can be seen again more aggressively after surgical removal. Injection sarcoma, like any type of cancer, can be seen in cats or dogs. Viral fibrosarcomas have been encountered for decades. Vaccine- or injection-related fibrosarcoma formation is relatively new. There are various discussions regarding this.

According to some studies, an increase in injection sarcomas has been seen with the requirement of rabies vaccine. The lower incidence of injection sarcoma in areas where rabies is not available or vaccination is not mandatory also supports this view. Sarcoma usually occurs between the shoulders or in the hind legs. These areas are known as common vaccination and injection areas. However, these are all controversial cases and their research continues.

What Causes Injection Sarcoma?

One theory about injection sarcoma is that after a vaccine, the immune system rushes to fight the vaccine site, and the resulting inflammation causes the cells to become cancerous and form tumors. However, it is one of the theories that the scar tissue becomes cancerous as a result of vaccination in the same area every year. The last theory about sarcoma formation is related to the content of vaccines. Vaccines do not contain live viruses. Instead, vaccines contain aluminum, which, according to some experts, can cause injection sarcoma. However, the exact cause of injection sarcoma is unknown, although there are 3 theories.

dog lying on sofa

How Common is Injection Sarcoma in Cats and Dogs?

Although injection sarcoma can occur in both cats and dogs, it is extremely rare in dogs. Injection sarcoma is not a common situation to be afraid of or to give up vaccination. There are studies showing that injection sarcoma is seen between 1 in 1000 and 1 in 10,000. On average, a cat needs to be vaccinated about 3 times a year. Considering that the average life span of cats is 15 years, it can be calculated that they will have a total of 45 vaccinations. This makes sarcoma extremely rare. Sarcoma formation can occur 2 years after the vaccine as well as 10 years later. However, the average duration of sarcoma is 4 years. 80% of the tumors that occur in injection sarcoma are fibrosarcoma, although rare, malignant soft tissue tumors, osteosarcoma, rhabdomyosarcoma, liposarcoma, chondrosarcoma or non-differentiated sarcoma can also be seen. All these tumors are muscle, bone, fat or soft tissue tumors.

Injection Sarcoma Symptoms

The biggest symptom of injection sarcoma is gland-like swellings that occur at the injection or injection site. Sarcoma usually does not have any other symptoms. Other symptoms usually occur after cancerization and spread. Acceleration of the heart rhythm, pallor of the lips, eyes and gums, fatigue, extreme weakness, dark urine, nosebleeds, blood in the urine or stool are among the main symptoms.

cat lying in bed

How to Track Injection Sarcoma?

There is a fairly easy method to follow the injection sarcoma called the 3 – 2 – 1 rule. It is perfectly normal to have swelling at the injection site, usually after vaccination. Swelling occurs due to the immune system’s response to the vaccine and inflammation in the area. Although these swellings do not mean fibrosarcoma, they disappear spontaneously in a short time. Fibrosarcoma takes years to form. The first point to consider in the 3 – 2 – 1 rule is how much time has passed since the vaccine. If there is still swelling at the injection site 3 months after vaccination, it may be necessary to remove the swelling or perform a biopsy. The second point is size. If the swelling is larger than 2 cm in diameter, it should be removed regardless of the vaccination date. The last rule is about the growth of the swelling. If the swelling is getting bigger instead of getting smaller 1 month after it is noticed, a biopsy should be done. The 3 – 2 – 1 rule briefly states that it should continue to grow 3 months after vaccination, 2 cm in diameter and 1 month after detection.

How is Injection Sarcoma Diagnosed?

When symptoms are suspected, veterinarians can make a definitive diagnosis with various methods. Today, injection sarcoma formation can be observed with advanced imaging methods such as MRI or computed tomography and biopsy. Contrast agents are used for good imaging. In this way, the location, size and shape of the sarcoma can be determined precisely. As a result of the examinations, it can be explained exactly how deep the sarcoma goes, which is extremely important.

Injection Sarcoma Treatment Methods

The only effective treatment for injection sarcoma is surgical intervention. Because it goes deep and is an aggressive tumor, it must be removed. In the meantime, it may become necessary to remove some of the healthy tissue around the tumor. If sarcoma occurs in the limbs, the limb is completely removed. Because the risk of recurrence after removal of the sarcoma is quite high. Therefore, radiation therapy can be applied before and after the operation. With radiation therapy after the operation, the development of cancerous tissues remaining in the body, if any, should be prevented. Chemotherapy does not provide any effect. However, even after treatment, the chances of survival of cats or dogs are low. Since it is an extremely aggressive tumor, it can often be seen again.

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