Home › Animalia › Animal health › Animal diseases › Sarcoma at the injection site

other disease Cat

Sarcoma at the injection site

This is a tumor that develops under the skin where an injection was given months, sometimes years earlier. It is rare, but it has the particularity of growing locally in a very infiltrative way: it sends extensions into neighboring muscles,...

Find a veterinarian All cat diseases

Definition Signs Causes Diagnosis Treatment Prevention Vaccination Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

This is a tumor that develops under the skin where an injection was given months, sometimes years earlier.

It is rare, but it has the particularity of growing locally in a very infiltrative way: it sends extensions into neighboring muscles, well beyond what we feel under the fingers.

This risk is known and documented. It does not call into question vaccination: the diseases avoided by feline vaccines are frequent and serious, and the benefit of vaccination remains far greater than this risk. What this observation has changed is the injection practices, not the decision to vaccinate.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Related signs — each one links to its page:

Nodules under the skin Swelling Pain Non-healing wound Weight loss Reduction

A firm mass under the skin, at a usual injection site: between the shoulders, on the side, or on a limb.

It is generally painless at first, attached to deep tissues, and grows slowly then faster.

The skin covering it can eventually ulcerate and ooze.

Pain, difficulty walking or lameness when the mass sits on a limb and invades the muscles.

Please remember: a small transient swelling after an injection is common and disappears within a few weeks. What should alert you is a mass that persists, grows or becomes bulky.

When to consult without delay

This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.

Causes and risk factors

The mechanism retained combines prolonged local inflammation at the injection site and cancerous transformation of the cells of the supporting tissue.

Several injectable products are affected, not just vaccines: certain depot anti-inflammatories, long-acting antibiotics and other products have been reported.

Vaccines containing adjuvants, intended to strengthen the immune response, have been more questioned; vaccines without adjuvant exist today.

Individual susceptibility is probable: the vast majority of vaccinated cats will never develop this tumor.

Repeated injections in the same place on the body.

Injectable products causing marked local inflammation.

A significant and lasting inflammatory reaction after an injection.

No race or gender is clearly predisposed; The tumor mainly affects adult and elderly cats.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

The veterinarian measures the mass, notes its exact location and mobility, and asks about the history of injections.

A simple recommendation, retained by groups of feline experts, guides the decision: a mass at the injection site which persists for more than three months, which exceeds two centimeters, or which continues to grow one month after the injection must be analyzed without delay.

The diagnosis is based on a tissue sample. Please note: the biopsy must be planned with the upcoming surgery, as the needle path or incision will need to be removed during the operation.

Cross-sectional imaging – CT or MRI – is very useful before the operation: it alone shows the true extent of the tumor, always larger than what is palpated.

Chest x-rays look for distant extension.

Never have a suspicious mass removed “just to see”: a poorly prepared first surgery seriously compromises the chances of recovery.

Treatment

Surgery is the main treatment, and the first operation is the most important: it must be wide and deep, removing a generous margin of healthy tissue all around the tumor.

It is a major surgery, often entrusted to an experienced surgeon, which may require removing muscle, part of the shoulder blade or a rib, or even amputating a limb when the tumor is located there.

Radiotherapy, before or after the operation, reduces the risk of local regrowth when it is accessible.

Chemotherapy is offered in certain situations, especially when the tumor cannot be completely removed or has spread.

Pain management and scar monitoring are an integral part of the treatment.

Regular monitoring of the operated area is essential: local regrowth is common and is better treated if it is caught early.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

Continue to vaccinate your cat. Coryza, typhus, leukosis and rabies are common or fatal diseases, and vaccination remains largely beneficial in view of this rare risk.

What can be prevented are the circumstances: the veterinarian adapts the choice of vaccines to the cat's real lifestyle rather than administering everything systematically, and spaces out the boosters according to the recommendations in force.

Good injection practices are established: vary the site for each injection, prefer low areas on a limb or on the flank rather than between the shoulders, and note in the notebook the exact location used.

Non-essential injectable products are avoided, and depot forms reserved for cases where they provide real benefit.

At home, pass your hand over your cat after each vaccination and check that any swelling disappears in the weeks that follow.

Vaccination

The link between certain injections, including vaccines, and this tumor has been established. It did not lead to giving up vaccination, but to practicing it differently.

Current recommendations are based on three principles: only vaccinate against what is useful to the cat concerned, respect the recommended intervals without multiplying injections, and inject at varied and identifiable sites.

Essential vaccines – typhus, coryza – remain recommended for all cats, including those who live in apartments. Leukosis affects those who go out or live in groups. Rabies follows current regulations and travel requirements.

If your cat has already had this type of tumor, do not decide alone to stop all vaccinations: the veterinarian will evaluate the benefit-risk ratio with you, cat by cat.

Possible complications

Local regrowth after surgery, particularly when the first operation was not large enough.

Remote extension, particularly towards the lungs, less common but possible.

Serious after-effects of surgery: extensive wound, difficult healing, loss of function of a limb.

Chronic pain if the tumor invades the muscles or bones.

When to see a veterinarian

You feel a mass under the skin where your cat received an injection.

This mass is still there more than three months after the injection.

It exceeds two centimeters or continues to grow one month after the injection.

The skin covering it breaks open, oozes or bleeds.

Your cat limps or seems painful in this area.

If in doubt, have it checked: a benign mass can be reassured in a consultation, a serious mass is treated much better early.

Prognosis

The prognosis depends above all on the quality of the first surgery and the real extent of the tumor.

A wide excision, prepared by cross-sectional imaging and supplemented by radiotherapy when available, offers the best chance of lasting control.

A tumor that is operated on insufficiently often grows back, and each surgical revision is more difficult than the previous one.

Distant extension remains less frequent than the local problem, which is the real issue with this disease.

Frequently asked questions

Should I stop vaccinating my cat?

No. This tumor is rare, while diseases prevented by vaccination are common and sometimes fatal. The benefit of vaccination remains far greater than the risk. Discuss with your veterinarian which vaccines are really useful for your cat and the frequency of boosters.

Is a small lump after a vaccine always worrying?

No. A firm, painless local reaction is common after an injection and disappears within a few weeks. What should lead to consultation is a mass that persists beyond three months, exceeds two centimeters or grows.

Why does my veterinarian vaccinate on the paw or flank?

Because a tumor that appears in this location can be removed widely, which is impossible between the shoulders where the surgery hits the spine and the ribs. Noting the site used also allows you to know later which product was injected where.

Why not just remove the ball and then see?

Because this tumor extends far beyond what we feel. Insufficient excision leaves cells in place, promotes regrowth and greatly complicates the following surgery. The first operation must be planned as the right one.