Feline cancers
Cancer is the uncontrolled growth of cells due to damage to DNA (mutations) and, occasionally, due to an inherited propensity to develop certain tumours. Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body - in other words, the body attacks its own cells. In contrast, transplant rejection happens because a normal healthy human immune system can distinguish foreign tissues and attempts to destroy them. Also the reverse situation, called graft-versus-host disease, may take place1.
Broadly, most chemotherapy drugs work by impairing mitosis (cell division), effectively targeting fast-dividing cells. As these drugs cause damage to cells they are termed cytotoxic. Some drugs cause cells to undergo apoptosis (so-called "cell suicide").
Unfortunately, scientists have yet to be able to locate specific features of malignant and immune cells that would make them uniquely targetable (barring some recent examples, such as the Philadelphia chromosome as targeted by imatinib). This means that other fast dividing cells such as those responsible for hair growth and for replacement of the intestinal epithelium (lining) are also affected. However, some drugs have a better side-effect profile than others, enabling doctors to adjust treatment regimens to the advantage of patients in certain situations.
As chemotherapy affects cell division, tumours with high growth fractions (such as acute myelogenous leukemia and the lymphomas, including Hodgkin's disease) are more sensitive to chemotherapy, as a larger proportion of the targeted cells are undergoing cell division at any time.
Chemotherapeutic drugs affect "younger" tumours (i.e. more differentiated) more effectively, because mechanisms regulating cell growth are usually still preserved. With succeeding generations of tumour cells, differentiation is typically lost, growth becomes less regulated, and tumours become less responsive to most chemotherapeutic agents. Near the centre of some solid tumours, cell division has effectively ceased, making them insensitive to chemotherapy. Another problem with solid tumours is the fact that the chemotherapeutic agent often does not reach the core of the tumour. Solutions to this problem include radiation therapy (both brachytherapy and teletherapy) and surgery.
| Adenocarcinoma (pulmonary) | a rare and usually fatal disease in cats |
| Basal cell tumours | a common cell tumour of the skin with variable malignancy |
| Bladder (urinary) cancers | a rare form of cancer in cats |
| Brain tumours | a rare form of cancer in cats, usually untreatable |
| Chemodectomas | a rare tumour of the aortic body, common in cats living at high altitudes |
| Chondrosarcoma and other 2ry bone cancers | a rare tumour of cartilage which affects the nasal cavities and surrounding sinuses. |
| Digit (paw) tumours | rare tumours affecting the feet of cats, usually requiring surgical excision |
| Ear tumours | common, fast growing tumour of skin inside the ear canal. Surgical excision is preferred treatment |
| Epulides | a tumour of the oral gums, often malignant in cats |
| Fibrosarcoma | a rare skin cancer associated with reactions to feline vaccines containing adjuvants. |
| Fibropapilloma (sarcoids) | a rare skin cancer often seen in farm cats |
| Globus tumours (pericytomas) | a rare tumour of blood vessels with high malignancy |
| Hamartoma | a rare vascular malformation/cancer in cats |
| Hemangiosarcoma | a rare and often fatal blood cell cancer |
| Histiocytic disease | a rare tumour of skin, showing as single or multiple nodules |
| Lipoma | a tumour composed entirely of fat cells. Rarely malignant. Surgical excision is preferred treatment |
| Leukaemia | a rare type of cancer, often associated with infection with FeLV virus |
| Lymphangiosarcoma | a tumour of the lymph system, with high malignancy and morbidity |
| Lymphoma | a cancer of lymph nodes, similar to Hodgkin's Disease in humans |
| Lymphosarcoma | one of the most common types of internal cancers in cats, usually in cats over 8 years of age |
| Mammary gland tumours | a common tumour in queens requiring mastectomy. |
| Mast cell tumours | a common skin tumour which can metastases but usually has a good prognosis post-surgical excision |
| Melanomas | a rare skin cancer with high mortality rates |
| Multiple myeloma | a rare, fatal tumour of plasma cells in cats |
| Osteosarcoma | a rare bone cancer affecting limbs of the cat, usually malignant. |
| Pancreatic tumours | usually malignant, rapid onset and high mortality rates in older cats |
| Papillomas / Papillomatosis | usually benign tumours of mouth and feet |
| Paraneoplastic syndrome | a neoplasia-associated alteration in bodily structure / function distant to the tumour |
| Plasmacytoma | a rare skin cancer of cats |
| Squamous cell carcinoma (skin cancer) | the most common and treatable form of cancer in cats |
| Teratoma | a rare cancer formed from germ cells |
| Testicular cancers | primarily Sertoli cell cancers, usually malignant |
| Thymoma | a relatively benign tumour of the thymus causing general physical disease |
| Thyroid hyperplasia (Hyperthyroidism) | a benign thyroid tumour readily treated with medication and/or radiation therapy |
| Urinary cancers | a rare form of cancer in cats |
| Vaccine- and microchip-associated sarcomas | a cancer as a result of certain types of vaccines |
In the past two decades, numerous experimental, clinical, and epidemiologic studies have linked tumour development and progression with the presence of cyclo-oxygenase (COX) in tumour cells in humans. A similar relationship between inflammation and oncogenesis seems to occur in cats associated with sarcomas and vaccines/microchips. COX enzymes exist as two different isoforms and catalyse conversion of arachidonic acid to an array of prostaglandins. COX-1 is expressed constitutively in many cells and is involved in normal physiologic activities such as cytoprotection of the gastric mucosa, regulation of renal blood flow, and platelet aggregation. COX-2 is an inducible enzyme that is involved in the production of prostaglandins, which modulate pathologic events such as inflammation, wound healing, and neoplasia. A variety of agonists including cytokines, growth factors, and oncogenes can induce COX-2 expression. COX-2 immunoreactivity is found in a number of human tumours including colon, lung, breast, gastric, prostatic, head and neck, and bladder carcinomas. More recently, COX-2 has been demonstrated in canine squamous cell, renal cell, and transitional cell carcinomas, prostatic adenocarcinomas, and intestinal neoplasias.
Recent studies also demonstrate that non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit COX enzymes, can reduce the incidence of cancer in humans and experimental animal models and may be potential targets for therapeutic and preventive strategies. Importantly, the relative risk of developing epithelial cancer, including colonic carcinoma, is lower in persons receiving aspirin therapy. In veterinary medicine, dogs with transitional cell carcinoma of the urinary bladder may have complete or partial reductions in tumour size when treated with piroxicam, a potent NSAID. Recently, anti-tumour activity was reported in dogs with oral squamous cell carcinoma treated with piroxicam2.
2.