Neoplasm in a dog
BY-Chakravarthi.R,
Final year BVSc and AH, Madras Veterinary College, Chennai-07.
India is a nation, where in general we treat nature as Gods and Goddesses. Cow is respected to ‘Komatha’, even we pray serpents but to an exception, we consider companion animal as family member, especially dogs, we could see elderly people treating them as own child, we could relate the grievances a family would face if they lose a four legged family member. Dogs are linked to human so emotionally that their bond remains inseparable. Today, comparing with past decades, the number of cancer cases increasing tremendously not only in humans but also in dogs. So let us go through cancer conditions by which a dog may get affected which remains as higher rate causing mortality in the dogs. The order in which the tumour conditions are arranged is based upon their incidence rate in descending order.
CANINE MAMMARY NEOPLASM:
One of the common neoplasm condition occurring in dogs with higher incidence of rate. The etiology of this condition is more similar to human mammary neoplasm, mis-sense mutation in 19th loci Single Nucleotide Polymorphism of BRCA2 gene. Symptomatically we can find out the condition by enlarged, hardened mass palpable in the mammary gland. The age-wise and sex-wise inheritance can be explained through expression of Estrogen receptors, HER2 receptors and Progesterone Receptors. To the question whether mammary neoplasm can occur in male dogs, the answer is ‘Yes’ in rare case scenario. Today diagnosing a dog with mammary neoplasm is not a great deal, it can be corrected through Surgical Ressection or Chemotherapy with anti-neoplastic drugs (Paclitaxel, Doxorubicin) and cox-2 inhibitors like Deracoxib. The main method of prevention is neutering or spaying the female dog before the first heat.
TRANSMISSIBLE VENEREAL TUMOUR:
This tumour condition is one of the common Sexually Transmitted Disease in dogs holding transmission route similar to Syphilis and Gonorrhoea. The etiology of this neoplasm traces back to 11,000 years ago where a dog with low genomic heterozygosity acquired this disease, since it is sexually transmitted it remain in the population. This tumour condition leads to bleeding from external genitalia frequently, this may be mistaken for estral bleeding in females and cystitis in males but on eversion of prepuce in males and on examining vaginal mucosa, we can see cauliflower-like pedunculated mass with bleeding from with. Note the examination must be carried out only with gloved hand in case of suspicion. So as like mammary neoplasm, diagnosing TVT is also more common in dogs, Treatment with Antineoplastic drugs like Vincristine as per protocol in case of small mass or surgical resection may be adopted if the mass is big. Cutaneous and ocular forms are also reported very rarely due to metastatic infiltration. Prevention is as simple, chain your pet dogs to avoid unwanted breeding with stray dogs. ‘ Prevention is always better than cure’.
LYMPHOMA:
As name suggests it is a cancer affecting the lymphatic tissues. It may be multicentric, mediastinal, alimentary or extranodal in nature.The etiology of Canine Lymphoma accounts to carcinogenic mutations in multiple genes particularly TRAF3, TRAF2, BIRC2, BIRC3, MAP3K14 and FBXW7, in a similarity with human lymphoma which also occurs due to mutation in multiple genes, a few may be NLRP5, NLRP14, and GRIFIN. Diagnosis is mainly based on visualisation of soft fluctuating mass beneath the shin. Majorly Lymphoma may be classified into two types for therapeutic purposed using Immunohistochemistry with markers CD3 and CD79 for B cell and T cell Lymphoma respectively. Treatment of multicentric lymphoma are often given the chemotherapy protocol UW-25, which is based on the CHOP protocol used in humans, whereas the chemotherapy protocol thought to be most effective at treating cutaneous lymphoma is lomustine. Having your dog diagnosed with Lymphoma that too T cell Lymphoma is seriously a bad news as the prognosis is poor.
ADENOCARCINOMA:
The incidence in dogs is low in comparison to people. The etiology traces back to carcinogenic mutations. These tumors tend to occur in older dogs (>9 years) and signs vary from anorexia, vomiting, weight loss, lethargy to diarrhea. Ultrasonography is the best diagnostic tool for identifying Intestinal Adenocarcinoma where the lesions found are thickening of intestinal wall upto 23 mm in some cases upto 63 mm, accumulation of fluid before the lesion site and loss of wall layering and cellularity. The main method of treatment is surgical resection. With adenocarcinoma, surgery is generally followed with chemotherapy using a drug called adriamycin (doxorubicin) +/- cytoxan, or in some cases, carboplatin.
PERIANAL ADENOMA:
Perianal adenoma (also known as circumanal adenoma and hepatoid adenoma) is a common tumor that arises from the sebaceous glands surrounding the anus. These tumors occur more common in intact males so if your dog is not used for breeding purpose neutering it at the early ages may be the method of prevention.Cocker Spaniel, German Shepherd and Bull dog breeds are affected in general. The main symptom observed is the presense of rounded, fluctuating mass in perianal region, constipation may occur due to obstruction of anal sphincter. Malignant form of this condition is perianal adenocarcinoma however this condition is very rare. It is confirmed by taking Fine Needle Aspiration Cytology. Surgical resection is the main method adopted.
LIPOMA:
Lipoma as name suggests in cancer occurring due to infiltration of fat cells. Again interestingly Lipoma in dogs share cytogenetic variation such as trisomy as in human lipoma. Lipoma is generally presented as a benign, soft fluctuating mass present as a hemispherical lump in the skin. It can be confirmatively diagnose by presence of fat cells in Fine Needle Aspiration Cytology. The treatment opted is surgical resection.
MASTOCYTOMA:
20% of skin Tumours identified in dogs were of Mastocytoma, benign in origin but rarely cells may infiltrate adjacent tissues with lower metastasis rates. Genetic predisposure of certain breeds like Boxer, Boston Terrier, Labrador, Golden retriever, Bull Terrier. Golden/ Red coat colour predisposes for Canine Mastocytoma. Mutagenic changes in CD 34+ pluripotent haemopoietic stem cells and c-KIT gene mutation and elevated c-KIT mRNA expression are the genomic changes observed and reported. The dog may have a tumour similar to that of Lipoma symptomatically but Fine Needle Aspiration Cytology reveals the presence of ‘crescent-shaped’ mast cells. Main treatment adopted is Surgical resection. Other therapies reported are Radiation Therapy, Oncolytic Sendhai Viral therapy, Photodynamic Therapy and Cryotherapy.
HISTIOCYTOMA:
Abnormal proliferation of Histiocytes , a cell found in skin tissue, leads to a rare condition called Canine Cutaneous Histiocytoma. These tumour occur as small solitary hairless lumps in face, neck and limbs. They are benign in nature having Labrador Retrievers and Boxers as predisposed breeds. The diagnosis is through Fine Needle Aspiration Cytology. This type of tumor have reports of regression with time but surgical resection may attempted if tumour size exceeds.
HEPATOCELLULAR CARCINOMA:
A very rare malignant tumour condition affecting the liver of dogs with higher metastatic rates. The main symptom may be gastrointestinal disturbance, pain in abdomen. The dog may be diagnosed through ultrasonography, a heterogenic mass will be visualised in affected lobe. Laparatomy and surgical resection is the treatment opted. However having your dog diagnosed with Hepatocellular carcinoma is not a great news as it have higher mortality rate though the incidence is very low. In contrary Humans, the condition occurs as a result of liver cirrhosis in major cases.
TRANSITION CELL CARCINOMA:
Cancer affecting the urinary bladder of dogs. As in humans , exposure of carcinogenetic substance in urine and mutation in BRAF gene may presumably be the cause of this neoplasm. The main symptom is being blood in urine. Diagnosis is done through radiographs, ultrasonography and urinalysis. Partial or complete resection of bladder is the surgical remedy however Quality Of Life in such cases may be compromised. Permanent catheterisation may be warranted. Other remedies reported are Chemotherapy with Carbaplatin and Deracoxib and Radiation Therapy targeting bladder.
OSTEOSARCOMA:
A very rare condition seen commonly affecting young children and dogs, sharing common etiology: Hypermutation and abundant Copy Number Variations in genes like TP53 and RB1 is Osteosarcoma. Recurrent mutations in DMD and the histone methyltransferase gene SETD2 are also reported to the genetic predisposition of the condition. Most commonly encountered in giant breeds of dog. Often found affecting bones of limb but sometimes it may affect skull, spine and ribs too but in rare case scenario. Radiographs and Computerised tomography are found effective in diagnosing the tumour. It is highly metastatic so the surgical remedy considered is amputation of affected region of limb.
Papilloma:
Papilloma is a benign skin tumour known as warts sharing common etiology with human papilloma, a viral origin. In dogs, it is reported to be caused by Canine Papilloma Virus-1. Common site of occurrence is multiple oral papilloma, solitary cutaneous papilloma, venereal mucosa papilloma and Eyelid papillomas. Reported commonly in young dogs. Papillomas generally regress within 2-3 months as the dog may develop immunity to it. However care must be taken as putting the dog in Elizabethian collar may reduce the chances of scratching which may lead to ulceration and delayed healing.
REASON FOR BREED PREDISPOSITION IN CANINE NEOPLASM:
On talking about Breed predisposition of cancer it is mainly due to the fact that gene inheritance in dogs breeds is Claudogram based that is dog breeds are grouped based on inheritance as Wolves, Mastiff- like dogs, Ancient and Spitz breeds, Toy breeds, Spaniels, Scent Hounds, Sight Hounds, Working dogs, Retrievers, Small Terriers and Herding dogs. They share common genes, so mutation if any get inherited into particular dog breeds belonging to same sub groups based on genetic relationships established.
INTERVENTIONS IN CANINE NEOPLASM:
Surgical Ressection is the common intervention preferred in Canine Neoplasm where the resection carried out by excision of tumour mass along with 2-5 cm margin of unaffected tissues as the cancer cells are highly infiltrating, in a view of reducing the incidence of recurrence. Radiotherapy and Chemotherapy may be adopted for some neoplasm specifically. Other practice followed is Cryotherapy which is indicated for reduction in size of tumour mass for which Liquid Nitrogen, care must be taken that during the procedure the unaffected tissues must be covered with polystyrene or surgical lubricant impregnated gauze.
Newer anti-neoplastic therapies reported are Photodynamic therapy that uses Photosensitizing substance such as Photofrin, Visudyne, Photochlor and Azadipyremethenes and molecular oxygen to ellucit Cell death to proliferating cancer cells. Oncolytic Sendhai virus and adeno virus may used therapeutically that aims Oncolysis on the basis of three properties
1. Unmasking Anti-cancer antigens, 2. Producing Interferon and 3. Stimulation of Natural Killer cells.
On concluding the article, different neoplasm conditions affecting the dogs, their etiology, predisposition, diagnosis, treatment and prevention are discussed briefly in this article. The relationship between Human Neoplasm and Canine Neoplasm are also discussed. Some tumour condition like Canine Mammary neoplasm not only shares genetic relationship but also shares histopathological and Immunohistochemistry relationship with Human Mammary Neoplasm to a greater extent which enables dog as the most preferred animal model for Human Cancer Research.
“Saving one animal will not change the world but the world may change for that animal.”
