FAQ – Cancer in Dogs and Cats | Veterinary Oncologist Warsaw

Squamous cell carcinoma / SCC | Borys

17 September 2021

A diagnosis or suspicion of cancer in a four-legged family member is hugely stressful for any owner. Below we have gathered answers to the most important questions about diagnostics, the course of chemotherapy and the early signs of cancer in dogs and cats, based on current medical knowledge and scientific publications.

Author: Anna Jaśkiewicz, DVM, PhD – veterinary oncologist, Warsaw

Suspected cancer in a dog or cat – what to do and which tests are needed before seeing an oncologist?

The foundation of effective cancer treatment is precise diagnostics. When a general practice veterinarian suspects cancer in your pet, have the widest possible set of additional tests done before the oncology consultation: a biopsy of the growth (cytology), an abdominal ultrasound and a full blood test. Bring this complete set of results to a specialist consultation with a veterinary oncologist.

In clinical practice we very often see skin or subcutaneous lumps that, without proper diagnostics – based only on palpation – are “monitored” for many months. This approach is highly risky. We recommend cytology (fine-needle aspiration, FNA) of every palpable skin lesion that persists for longer than 4 weeks. Microscopic assessment of cells collected from the lump allows a preliminary diagnosis to be made quickly and targeted treatment to be planned.

What are the most common cancers in dogs and cats?

The latest veterinary statistics indicate that one in four four-legged patients will be diagnosed with cancer during their lifetime. It is the leading cause of death in dogs and cats past middle age [1, 2].

The most commonly diagnosed cancers in dogs and cats include:

Lymphoma – accounts for 7 to 24% of all cancers in dogs and as much as 83% of all haematopoietic cancers; it is diagnosed just as often in cats [3, 4].
Osteosarcoma – the most common primary bone tumour, accounting for as much as 85% of all neoplastic lesions of the skeleton [5].
Mast cell tumour (mastocytoma) – the most common skin tumour in dogs and the second most common skin tumour in cats [6].
Oral melanoma and squamous cell carcinoma (SCC) – melanoma is seen far more often in dogs [7], whereas in cats malignant squamous cell carcinomas predominate in the oral cavity [8].
Hemangiosarcoma – an aggressive cancer most often described in dogs, accounting for 45 to 51% of all splenic tumours [9].
Transitional cell carcinoma of the urinary tract (TCC / UC) – accounts for around 2% of all cancers in dogs [10] and is the most common malignant tumour of the bladder and urinary tract.

How to prepare a dog or cat for chemotherapy?

The most important part of preparing an animal for chemotherapy is an up-to-date blood test (complete blood count) – done no more than 24 hours before the planned visit or at the clinic directly before the drug is given. It allows the veterinary oncologist to assess the condition of the bone marrow and safely qualify the patient for cytostatic drugs.

Once the diagnostic process is complete and a diagnosis has been made, the veterinary oncologist prepares an individual treatment plan. Chemotherapy is the main method of systemic treatment, consisting of cytostatic drugs that destroy cancer cells or stop them from dividing. Bear in mind that cytostatic drugs target rapidly dividing cells – besides cancer cells, these also include normal bone marrow cells. For this reason, transient anaemia or a drop in white blood cell count may occur during therapy, which requires regular blood count monitoring before each subsequent infusion.

What else should you remember before the oncology visit?

Complete medical records: the treatment plan must take concurrent diseases into account, so bring your pet’s entire treatment history to the consultation.
Stress reduction (especially in cats): if your pet gets very stressed by travel or by examination in the consulting room, ask the oncologist for safe calming medication (oral premedication) that you can give at home before leaving for the clinic.

Is chemotherapy for a dog or cat safe for the owner, children and household members? Can the pet be stroked?

Yes, contact with an animal during chemotherapy does not pose a significant risk to healthy household members, and dogs and cats can be stroked and cuddled as normal, because cytostatic drugs are not excreted through the skin or fur. However, stricter hygiene is necessary when cleaning up excreta for the first 3–4 days after the drug is given.

Although the cytostatic drugs used in veterinary oncology originate from human medicine, our patients receive them in doses calculated strictly according to their body weight – very small amounts relative to the body weight of an adult human. During treatment the animals function normally at home and do not require hospitalisation.

Safety rules at home for 3–4 days after chemotherapy is given:

Excreta and secretions: for up to 72–96 hours after the procedure, drug metabolites may be present in the animal’s urine, faeces, vomit and, to a lesser extent, saliva.
Hand hygiene and stroking: stroking your pet is completely safe. However, if the animal licks your hand, wash it immediately with warm water and soap.
Cleaning up waste: always clean up urine, faeces or vomit wearing disposable rubber or nitrile gloves, using paper towels. Seal the used materials in a tightly closed plastic bag and put it in an outdoor waste bin. For cats, thorough daily cleaning of the litter tray is recommended.
Groups at particular risk: pregnant women, breastfeeding women, couples trying to conceive, people receiving immunosuppressive treatment and small children should avoid direct contact with the animal’s excreta and limit close contact with the pet in the first days after the cytostatic drug is given.

Side effects of chemotherapy in animals – can the therapy be changed if the pet feels unwell?

Yes – if the animal tolerates the prescribed treatment poorly, the veterinary oncologist can reduce the dose, introduce protective medication, switch the protocol to a different drug or stop the therapy altogether. The overriding goal of veterinary oncology is to give the patient the best possible quality of life (feeling well, without pain) while also prolonging survival.

The word “chemotherapy” causes owners great anxiety, stemming from associations with human medicine. In reality, the vast majority of dogs and cats tolerate cancer treatment very well. Side effects occur in around 30% of patients and are usually mild to moderate – they mainly affect the digestive tract (transient diarrhoea, vomiting, reduced appetite). If you notice any worrying signs in your pet after the drug is given, contact the treating veterinarian so that the management can be modified immediately.

Do you suspect cancer in your pet or need a reliable diagnosis?
Early detection of a lesion is the key to effective treatment and your pet’s wellbeing. We offer specialist oncology consultations, fine-needle aspiration biopsies and safe chemotherapy for dogs and cats in Warsaw.

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First signs of cancer in dogs and cats – what are paraneoplastic syndromes?

The first changes occurring in an animal’s body under the influence of a developing cancer often take the form of so-called paraneoplastic syndromes (PNS). These are disorders in the structure or function of tissues and organs that do not result directly from physical pressure from the primary tumour or from the presence of metastases. Paraneoplastic syndromes arise because cancer cells secrete biologically active substances – hormones, cytokines or growth factors – that act on the patient’s whole body [11].

Early recognition of a paraneoplastic syndrome makes it possible to detect a hidden cancer process before the tumour becomes visible to the naked eye. Below we present the 9 most common signs and paraneoplastic syndromes that you may observe in your pet or in its blood test results:

1. Sudden weight loss and muscle wasting (cancer anorexia and cachexia)

Gradual weight loss – above all wasting of muscle tissue – is observed in 35% of dogs and cats with cancer as early as 12 months before the diagnosis is made [12]. In cats, a body condition score (BCS) below 5 on a nine-point scale is reported in 44% of oncology patients. Emaciation affects in particular cats with oral squamous cell carcinoma and gastrointestinal lymphoma, resulting from difficulty taking in and digesting food [13]. Loss of muscle mass in the course of cancer affects as many as 93% of feline patients and, regardless of tumour type, is associated with a poorer prognosis [13].

Learn more: you can read about the exact mechanism of weight loss in cancer patients in my peer-reviewed scientific paper in the journal International Journal of Molecular Sciences: view the scientific article (DOI: 10.3390/ijms21218261) →

2. Chronic vomiting and diarrhoea (gastrointestinal disorders)

If your pet is increasingly suffering from recurrent gastrointestinal problems, be sure to ask your veterinarian to extend the diagnostics to include a blood test and an abdominal ultrasound. Some cancers – above all mast cell tumours (mastocytoma) – release large amounts of histamine. Histamine stimulates the parietal cells of the stomach to secrete excessive hydrochloric acid, which leads to painful ulcers of the digestive tract, manifesting as reflux, chronic vomiting and diarrhoea [13].

3. Elevated blood calcium (hypercalcaemia)

If you notice a raised calcium level in your dog’s or cat’s follow-up blood results, this calls for an urgent oncology consultation. As many as 60% of dogs and 30% of cats with hypercalcaemia have cancer [14]. In dogs, raised calcium most often accompanies T-cell lymphoma and apocrine gland adenocarcinoma of the anal sac [15]. In cats, the main causes of cancer-related hypercalcaemia are lymphomas, squamous cell carcinomas and multiple myeloma [16]. This phenomenon results from cancer cells secreting mediators (e.g. the protein PTHrP) that increase the release of calcium from bone and reduce its excretion by the kidneys [16].

4. Low blood glucose (hypoglycaemia)

Cancer-related hypoglycaemia occurs most often in dogs with insulinoma – a tumour that secretes excess insulin [17]. A marked drop in blood sugar is also seen with primary liver tumours and tumours arising from the smooth muscle of the digestive tract, such as leiomyosarcoma and leiomyoma [18, 19]. In addition, hypoglycaemia may accompany hemangiosarcoma, lymphoma, leukaemia, mammary gland tumours, melanoma, plasmacytoma and adenocarcinomas of the kidney and salivary glands [20].

5. Symmetrical hair loss and hormonal changes (hyperoestrogenism)

Excess oestrogen is found most often in entire (uncastrated) male dogs that have developed testicular tumours – mainly Sertoli cell tumours (sertolioma). Clinically, feminising syndrome in a male dog presents as symmetrical hair loss on the flanks and thighs, dark discolouration of the skin (hyperpigmentation), enlargement of the mammary glands (gynaecomastia), prostatic enlargement and testicular asymmetry. In advanced cases, excess oestrogen leads to toxic bone marrow damage and life-threatening non-regenerative anaemia [21].

6. Hard-to-control diabetes and changes in head features (acromegaly)

Acromegaly occurs most often in cats with a pituitary adenoma that secretes excessive amounts of growth hormone [22]. It is seen less often in dogs, in which overproduction of growth hormone is induced by pituitary tumours or by progesterone produced by mammary gland tumours [23]. In cats, acromegaly presents as insulin-resistant diabetes, overgrowth of connective tissue and bone (broadening of the head features, forward protrusion of the lower jaw – so-called prognathism), enlargement of internal organs (liver, kidneys, adrenal glands) and hypertrophic cardiomyopathy [24].

7. Abnormalities in the blood count

A preventive blood test done once a year in middle-aged and older animals is the basis of early diagnostics. The first sign of a cancer process can be specific abnormalities in the blood count and biochemistry:

Hyperglobulinaemia (elevated levels of globulin proteins) – observed most often in multiple myeloma and lymphomas [25].
Anaemia – the most common haematological paraneoplastic syndrome, found in 30–43% of dogs and 43–58% of cats with lymphoma [26, 27], and also in leukaemias, hemangiosarcoma, disseminated mastocytoma and histiocytic sarcoma [28]. It results from bleeding (e.g. a ruptured splenic tumour), destruction of red blood cells (haemolysis) or impaired production in the bone marrow [29].
Erythrocytosis (polycythaemia – increased red blood cell count, haematocrit and haemoglobin) – accompanies kidney tumours, fibrosarcomas of the nasal cavity and spinal cord tumours as a result of excessive erythropoietin production by tumour cells [30].
Leukocytosis (marked increase in white blood cell count) – caused by inflammation or necrosis of tumour tissue. Neutrophilia, eosinophilia and monocytosis are frequently recorded in dogs with lung and kidney tumours, intestinal T-cell lymphoma and fibrosarcoma, and in cats with lung carcinoma and skin adenocarcinoma [28].
Thrombocytopenia (reduced platelet count) – occurs in around 36% of dogs and 39% of cats already at the time of the cancer diagnosis [31, 32].

8. Unusual skin problems and hair loss

Owners rarely link chronic dermatological changes with cancer of the internal organs. The most important cutaneous paraneoplastic syndromes include:

Nodular dermatofibrosis – observed primarily in German Shepherds with hereditary kidney tumours [33].
Superficial necrolytic dermatitis – affecting dogs and cats with liver and pancreatic tumours [34].
Feline paraneoplastic alopecia – occurring in cats with pancreatic adenocarcinoma and bile duct carcinoma; the hair loss is not itchy and mainly affects the underside of the trunk and the inner surfaces of the limbs [34].
Exfoliative dermatitis – characteristic of cats with thymoma; severe scaling of the epidermis and loss of fur affect the neck, trunk and limbs [34].

9. Sudden lameness and limb swelling (musculoskeletal disorders)

Painful limbs, symmetrical swelling and reluctance to move may be associated with the development of hypertrophic osteopathy (Marie-Bamberger syndrome) – a process involving painful subperiosteal new bone growth on the long bones [35]. Hypertrophic osteopathy most often accompanies primary lung tumours or advanced lung metastases [35]. In cats with primary lung carcinoma, on the other hand, unusual metastases to the bones of the digits sometimes occur (presenting as a swollen toe and lameness, often mistaken for a paronychia or a claw injury) – this phenomenon is known as feline lung-digit syndrome (FLDS) [36].

Have you noticed any of the signs above in your pet?
Do not wait for the disease to progress. Sufficiently early cytology, ultrasound and laboratory tests make it possible to choose a safe therapy precisely and to halt the cancer process. Consult your pet’s case with Anna Jaśkiewicz, DVM, PhD in Warsaw.