Comparative characteristics of treatment methods for melanoma in dogs. Melanoma in dogs and cats

Text of the article and photos 1-6 from the SMALL ANIMAL DERMATOLOGY A COLOR ATLAS AND THERAPEUTIC GUIDE 2017

Translation from English: veterinarian Vasiliev AB

Peculiarities

This condition is characterized by benign (melanocytoma) or malignant (melanoma) proliferation of melanocytes. Most cases (85%) are benign. Since melanocytomas and melanomas in dogs occur on hairy skin or in the oral cavity, sun exposure is not considered causative factor. Breed and familial prevalence in domestic animals suggests that there may be genetic predisposition to this pathology.

Changes in oncogenes, tumor suppressor genes and immunological surveillance are also involved in the development of this pathology. These tumors are common in older dogs and rare in older cats. Among the dogs predisposed breeds include Scotch Terriers, Airedale Terriers, Doberman Pinschers, Cocker Spaniels, Poodles, Irish Setters and Schnauzers.

Melanocytomas are usually solitary, well-demarcated, dome-shaped, firm, cinnamon or black, hairless, pedunculated or verrucous in shape, and vary in size from 0.5 to 10 cm in diameter. Plaque-shaped tumors may also occur. Malignant melanomas may be pigmented or non-pigmented (amelanotic), may be ulcerated, and tend to be larger and more rapidly growing than benign melanocytomas.

Malignant tumors tend to metastasize first to regional lymph nodes and then to the lungs. Lesions can be located on any part of the body, but in dogs they are most common on the head, trunk and fingers. In cats, lesions are most often found on the head.

Diagnosis

1 Cytology: round, oval, stellate or spindle-shaped cells with a moderate amount of cytoplasm containing granules of brown to greenish-black pigment. Malignant melanomas may have less pigment and exhibit greater pleiomorphism, but malignancy cannot be reliably determined cytologically.

2 Dermatohistopathology: accumulation of neoplastic melanocytes, which may be spindle-shaped, epithelial or round in shape with various degrees pigmentation. The cells may be grouped into clusters, cords, or whorls, similar to nerves. Infiltration by pigmented macrophages is often observed. Benign tumors are delimited and have low nuclear variability and low mitotic rates.

Malignant melanomas may show greater invasiveness, more extensive cellular pleiomorphism, and an increased number of mitotic figures (including atypical mitotic figures). The mitotic index is the most reliable way to predict biological behavior (mitotic rate<3 митозов/10 высокомощный полей обычно ассоциирован с доброкачественностью); однако,10% гистологически доброкачественных меланоцитом ведут себя как злокачественная опухоль.

3 In animals with malignant melanomas, regional lymph nodes and the chest and abdomen should be examined to identify metastases.

Treatment and prognosis

1 The treatment of choice is radical surgical excision because benign melonocytomas cannot be clinically differentiated from malignant melanomas.

2 If surgical excision is incomplete, additional treatment options include radiation therapy and local hyperthermia.

3 Chemotherapy (carboplatin, piroxicam and dacarbazine) can prolong survival in some cases of cancer, but in general the response to chemotherapy is poor.
4 Although it was primarily evaluated in canine oral malignant melanoma, Merial's xenogeneic DNA melanoma vaccine may be useful in controlling systemic metastases from cutaneous malignant melanocytomas.
5 Tomotherapy, an advanced form of radiation therapy that uses the precision of CT scanning technology, may in the future provide better outcomes than currently available treatments.
6 The prognosis is good for benign melanocytomas. The prognosis is poor for malignant melanomas, especially if the tumor is large, there is recurrence after surgery and metastasis. Tumor location is predictive: most oral and mucocutaneous melanomas (excluding eyelid tumors) and 50% of melanomas involving the claw beds are malignant. The breed is also prognostic: more than 75% of melanocytic tumors in Doberman Pinschers and Miniature Schnauzers are benign in behavior, and 85% of these tumors in Miniature Poodles are malignant in behavior.

Photo 1. Melanocytoma and melanoma of the skin of dogs and cats. A pigmented nodule near the nasal planum in an adult dog.

Photo 2. Melanocytoma and melanoma of the skin of dogs and cats. Focal pigmented nodule on the head of an adult dog.

Photo 3. Melanocytoma and melanoma of the skin of dogs and cats. Multilobulated hairless hyperpigmented melanoma on the head of an adult schnauzer.

Photo 4. Melanocytoma and melanoma of the skin of dogs and cats. Focal pigmented nodule.

Oncological diseases in human medicine are no longer an unambiguous verdict: statistics show that cancer, if it was not noticed at the last stage, is almost always cured. The situation with animals is not so rosy. Thus, melanoma in dogs still claims the lives of animals all over the world, so it is important for owners to know at least about the basic symptoms.

This is a malignant tumor, the basis of which is melanocytes. These are cells that lie in the deep layers of the skin, giving it color and also protecting it from excess ultraviolet radiation. It is this type of oncology that is most often detected in oral cavity dogs, this cancer is often found on the extremities of animals. An exceptional type is ocular melanoma in dogs.

Practice shows that males suffer from melanoma much more often than females. It is believed that Scottish setters, cocker spaniels, and golden retrievers are predisposed breeds. Tumors of this type are extremely dangerous, as they can penetrate deeply into the tissue, can affect bones, and also very often give metastases. In a word, you should under no circumstances delay their treatment.

Causes and symptoms

In humans, 90% of melanomas occur in those who spend a lot of time in the sun without using sunscreens. As for dogs, everything is not completely clear with them, since tumors appear even in those areas that are extremely rarely exposed to sunlight (the mouth, for example).

What are the symptoms of melanoma in dogs? The presence of visible swelling in the mouth is the most common sign. Increased drooling, swelling and swelling, weight loss, bad breath, pain, inability to eat, food falling out of the mouth and loose teeth are other characteristic symptoms. The color of tumors can be very different, ranging from pinkish to black.

The signs of this type of cancer on the extremities are similar. Firstly, a swelling of unknown etiology may also appear on the animal’s paw. Lameness and loss of claws are common signs. Tumors are most often black.

Diagnostic methods

Melanomas are diagnosed exclusively in the clinic. The veterinarian may use needle biopsy and cytology. To obtain pathological material, a needle of the required diameter is taken. Since there are a lot of nerve endings in the oral cavity, powerful sedatives must be used before this procedure. Otherwise, the dog will simply bite everyone present. If the suspected tumor is located on the leg, you also have to resort to pain relief.

Alas, a simple puncture biopsy cannot provide all the necessary information in all cases. In this case, you have to use local anesthesia again and cut out a piece of tissue at the border of the affected and healthy cells (this procedure is shown in the photo).

All dogs with this diagnosis should have regional lymph nodes and lungs checked for metastases. Regional lymph nodes are checked by needle biopsy and cytology (or biopsy under anesthesia). X-rays or CT scans are used to check the "clearness" of the lungs. Experienced specialists strongly advise checking the entire abdominal cavity, since metastases are often found there as well.

Read also: Facial paralysis in a dog: the entire muzzle, one side, tongue, jaw

Therapeutic techniques

What is the treatment for melanoma in dogs? First, the veterinarian must very carefully examine the location of the tumor, accurately identifying its boundaries. Unfortunately, if the melanoma is in the mouth, it almost never can be removed completely without affecting some of the bone. You should not assume that such an operation has a serious impact on the animal’s condition. Most dogs (>85%) will continue to eat, drink, chew, and play with toys. If melanoma has developed on the toe of one of the paws, it is completely removed. Chemotherapy significantly reduces the likelihood of relapse of the disease (but does not reduce it to zero).

The pharmaceutical company Merial (USA) has begun testing a drug that has already been dubbed a “vaccine against melanoma” (Oncept). Treatment is aimed at stimulating immune system, which (theoretically) should cope with cancer itself. The test results are already encouraging.

What about traditional chemotherapy? It can be used in cases where the tumor for some reason cannot be removed surgically, not sensitive to radiation therapy, or in case of detection of metastases. IN recent years New chemotherapy drugs that are less aggressive on the canine body are gradually becoming widespread.

In what cases can radiation therapy be used? In the same as chemical treatment: if surgery fails, or the melanoma is too serious. In most cases, radiation therapy is used after surgical intervention. This is done so as not to leave cancer cells in the body. Fortunately, global veterinary practice proves that melanomas are very sensitive to radiation exposure.

Canine melanoma is a malignant tumor that develops from melanocytes (pigment cells). Melanoma is characterized by the accumulation of melanin (a special pigment) in tumor cells, but so-called pigmentless melanomas also occur. Also, melanoma in dogs can be called melanoblastoma, melanocarcinoma or melanocytoblastoma, but in this article we will stick to the term melanoma adopted in our clinic.

Melanoma occurs in dogs on the skin, mucous membranes of the oral cavity, on the genitals, on the mucous membranes of the eyes and on the nasolabial planum. Rare, but spontaneous melanoma occurs internal organs containing melanocytes, primarily central nervous system(CNS) and intestines. This is due to the fact that melanocytes in dogs are found not only predominantly in the basal layer of the epidermis, but also in places such as choroid eyes, in the central nervous system at the junction of the soft and arachnoid membranes brain, into the epithelium of other organs - intestines, gallbladder, esophagus, anus, vagina. In our practice, canine melanoma of the mucous membranes of the oral cavity and conjunctiva is often encountered. The latter has a more favorable course, lower incidence of recurrence and metastasis. Melanoma of the oral mucosa in dogs is real problem. This is due, first of all, to poor visualization and late detection of the tumor, constant trauma to melanoma during the act of eating.

Causes of melanoma in dogs

The causes of melanoma in dogs vary. They include:

Physico-chemical factors - ultraviolet irradiation unprotected by fur skin, ionizing radiation, chemical carcinogens etc.
Biological factors - type of diet, presence of viral infections, whether the puppy has had severe illnesses viral infections, use of certain medications.

Socioeconomic factors that play a major role in the pathogenesis of human melanomas have not been reliably identified in dogs.

Oncogenes play a key role in the development of aggressive forms of melanoma in dogs. Mutations of the Ras protein family - NRAS, HRAS, KRAS, a mutation of the BRAF gene and expression (from the Latin expressio - expression) of the KIT proto-oncogene in exon 11 have been described. This KIT proto-oncogene in dogs encodes a transmembrane (membrane-transporting) tyrosine kinase receptor. Tyrosine kinases are specific protein molecules on the surface cell membranes, responsible for transmitting signals into the cell, primarily signals for division and differentiation. It is the disruption of cell division and differentiation that plays important role in the development of melanoma in dogs.

Symptoms of melanoma in dogs

Melanoma is manifested by the presence of a tumor mass on the skin or mucous membrane, often dark in color. The presence of uneven edges, erosions, and hemorrhages is noted. With the development of melanoma of the mucous membranes of the oral cavity in dogs, the appearance of thick, viscous saliva with a strong putrid smell, violation of the act of eating, spotting from the oral cavity.

Diagnosis of melanoma in dogs

When examining a dog with suspected melanoma, the doctor pays attention to the mobility of the formation, color, and the presence of damage to the skin or mucous membrane. Evaluates both regional and distant lymph nodes. Determines the presence of small pigmented and non-pigmented formations (satellites) near the tumor. Significant help in early diagnosis melanomas in dogs is the “ABDCE malignancy rule”:

A (asymmetry) - asymmetry, one side of the tumor is not similar to the other;
B (border irregulatrity) - unevenness of the edges of the tumor;
C (color) - the color of pigmented melanoma is not completely black, but has inclusions of blue, brown and even pink;
D (diameter) - tumor diameter more than 4 mm;
E (elevation) - raising the tumor above the surrounding tissue.

The next step in diagnosing melanomas in dogs is a fine-needle biopsy or cytological examination. This method easy to perform, quick and safe for the dog. When diagnosing melanomas, unlike other types malignant tumors in dogs, cytological analysis is highly accurate - the sensitivity of this type of research exceeds 94% (94.2%, Gelfond M.L., 2004).

Another type of morphological study of canine melanoma is histological examination. Material for this type of research can be obtained using the following methods:

Incisional biopsy - obtaining a small piece of tumor by cutting it off or biting it off with a special device under local anesthesia;
Excisional biopsy - excision of the entire tumor followed by histological examination;
Core biopsy - obtaining a column of material using a special biopsy gun.
Punch biopsy - obtaining a column of material using a special cylindrical scalpel.

When conducting histological examination melanomas in dogs, extremely important prognostic values are the determination of tumor thickness according to Breslow and the degree of invasion (germination) according to Clark. The thickness of the tumor according to Breslow is determined with a micrometer to the level of the basement membrane of the skin. Clarke invasion characterizes the depth of melanoma penetration into various layers of the skin. The prognosis of the animal’s life depends on this.

Methods are widely used to diagnose distant metastases in dogs. radiology diagnostics(X-ray) and ultrasound diagnostics(ultrasound). These types of examinations help to stage the disease and develop further treatment tactics and determine the prognosis.

After receiving all the data on the animal’s condition, the doctor begins to develop a treatment regimen.

Treatment of melanoma in dogs

Surgical treatment

Surgical treatment of melanoma in dogs is technically difficult and is primarily due to the fact that the tumor spreads far beyond its own borders. That is, such formations as melanomas are excised with a wide coverage of surrounding tissues. This technique suitable only for relatively small formations skin, where it is possible to perform plastic surgery to close the wound defect. This principle was developed at the beginning of the last century; the width of the surrounding tissue was recommended to be at least 2.5 cm. At the same time, it was recommended to simultaneously remove the regional lymph node for its subsequent histological examination.

Cryodestruction of melanoma

When melanoma is localized in the oral cavity, this principle cannot be observed and one has to resort to other methods of eliminating the tumor mass. The method of cryodestruction of melanoma has proven itself well - the effect on the tumor mass liquid nitrogen with the help special device, which leads to complete freezing of the formation. Repeating three cycles of freezing followed by thawing causes, in most cases, the complete disappearance of tumors in the oral cavity in dogs. Of course, this technique does not lead to recovery, but people often come to us with neglected cases when little can be done to improve the pet’s quality of life. This technique is ideally suited for these purposes - it is low-traumatic and does not cause severe pain after exposure and economically acceptable.

Radiation therapy for tumor

Another way to treat melanoma in dogs is to treat the tumor with radiation. However, melanoma is poorly sensitive to radiation and is only suitable for irradiating the tumor bed after its removal. This method of exposure is technically complex, expensive and is not often recommended by oncologists for the treatment of melanomas.

Chemotherapy

An additional method of treating canine melanoma is chemotherapy. The gold standard for chemotherapy for melanomas is the use of the drug Dacarbazine, but its effectiveness, according to humane medicine, does not exceed 15%. This low effect forces us to look for new methods of chemotherapy treatment. For example, the majority of human melanomas have a BRAF mutation, which has led to the use of drugs that block these mutations, such as Vemurafenib. In dogs with melanoma, the presence of a KIT mutation has been noted, which allows the use of tyrosine kinase inhibitors, such as Toceranib (Palladia), Masitinib (Masivet), Imatinib (Glivek). This group The drug blocks tumor cells that have this mutation, having a slight, unlike conventional chemotherapy, toxic effect on the body. Overall, the use of tyrosine kinase inhibitors in canine melanoma shows good promise.

Prognosis for melanoma in dogs

Canine melanoma has a poor prognosis - often due to its location in the oral cavity, which does not allow the owner to immediately notice the tumor, patients with distant metastases come to our clinic and full recovery there is no need to talk. All treatment comes down to making life as comfortable as possible, reducing pain, and increasing the patient’s activity. Today, the combination of cryodestruction, radiation therapy and targeted chemotherapy with tyrosine kinase inhibitors.

Clinical case of stabilization of melanoma in a Yorkshire terrier

A Yorkshire terrier named Venice (11 years old) was admitted with complaints of a large gum formation. A biopsy of the formation was performed. Based on histological and immunohistochemical analyses, a diagnosis of melanoma was made, ki-67 70%. This diagnosis is dangerous and has a negative prognosis. To improve the quality of life in Venice, a decision was made to undergo cryodestruction of melanoma. This procedure complex, lengthy and performed under general anesthesia.

After 10 days, complete disappearance of the tumor lesion of the jaw was noted - CR (complete regression) or CR (complete response):

Text of the article and photos 1-6 from the SMALL ANIMAL DERMATOLOGY A COLOR ATLAS AND THERAPEUTIC GUIDE 2017

Translation from English: veterinarian Vasiliev AB

Peculiarities

This condition is characterized by benign (melanocytoma) or malignant (melanoma) proliferation of melanocytes. Most cases (85%) are benign. Since melanocytomas and melanomas in dogs occur on hairy skin or in the oral cavity, sun exposure is not considered a causative factor. The breed and familial prevalence in domestic animals suggests that there may be a genetic predisposition to this pathology.

Changes in oncogenes, tumor suppressor genes and immunological surveillance are also involved in the development of this pathology. These tumors are common in older dogs and rare in older cats. Among dogs, predisposed breeds include Scotch Terriers, Airedale Terriers, Doberman Pinschers, Cocker Spaniels, Poodles, Irish Setters and Schnauzers.

Melanocytomas are usually solitary, well-demarcated, dome-shaped, firm, cinnamon or black, hairless, pedunculated or verrucous in shape, and vary in size from 0.5 to 10 cm in diameter. Plaque-shaped tumors may also occur. Malignant melanomas may be pigmented or nonpigmented (amelanotic), may be ulcerated, and tend to be larger and grow more rapidly than benign melanocytomas.

Diagnosis

2 Dermatohistopathology: accumulation of neoplastic melanocytes, which may be spindle-shaped, epithelial or round in shape with varying degrees of pigmentation. The cells may be grouped into clusters, cords, or whorls, similar to nerves. Infiltration by pigmented macrophages is often observed. Benign tumors are circumscribed and have low nuclear variability and low mitotic rates.

3 In animals with malignant melanomas, regional lymph nodes and the chest and abdomen should be examined to identify metastases.

Treatment and prognosis

1 The treatment of choice is radical surgical excision because benign melonocytomas cannot be clinically differentiated from malignant melanomas.

2 If surgical excision is incomplete, additional treatment options include radiation therapy and local hyperthermia.

Photo 1. Melanocytoma and melanoma of the skin of dogs and cats. A pigmented nodule near the nasal planum in an adult dog.

Photo 2. Melanocytoma and melanoma of the skin of dogs and cats. Focal pigmented nodule on the head of an adult dog.

Photo 3. Melanocytoma and melanoma of the skin of dogs and cats. Multilobulated hairless hyperpigmented melanoma on the head of an adult schnauzer.

Photo 4. Melanocytoma and melanoma of the skin of dogs and cats. Focal pigmented nodule.

Melanoma is a malignant tumor that develops in the melanocyte cells responsible for the production of melanin. If we talk about visual manifestation, more often it looks like a black or dark brown spot with jagged edges. It has a shiny surface and a tendency to disintegrate.

Melanoma in dogs is a fairly common disease that occurs more often than in cats. There are many photos on the Internet depicting the formation, so it is not so difficult for owners to determine that their pet requires immediate treatment. The main thing is to notice the stain in time and compare it with numerous photos.

Where does melanoma occur?

The problem can appear in any area of the eye:

eyelid;
conjunctiva;
cornea and sclera;
iris;
retina;
choroid.

Initially, the formation may be benign, but if the owner ignores this issue, it will turn into malignant.

Owners of cats and dogs should remember that the disorder generally begins to develop in animals between the ages of 8 and 10 years. By the way, this disease is more typical for males than for females. Predisposed to it:

poodle;
Scotch Terrier;
dachshund;
cocker.

These breeds have highly pigmented skin.

Causes, symptoms and diagnosis

Doctors have never been able to completely determine what exactly causes melanoma. Malignant cells form in melancytes and lead to DNA mutation. They multiply very quickly, turning healthy cells that should die over time into mutated ones.

To detect a disease in an animal in time, you need to pay attention to the following symptoms:

swelling of the eyelid and surrounding tissues;
corneal clouding;
red conjunctiva;
tears and other secretions;
the appearance of ulcers on the eyelid, bleeding;
decreased visual acuity;
the appearance of dark spots on the eye surface.

If the disease is not detected in time, it can develop into secondary glaucoma, uveitis, and intraocular hemorrhages.

Since this is a serious disease, careful diagnosis is required, which is carried out only in specialized clinics with the necessary equipment. To make a diagnosis, the following is performed:

visual assessment;
biomicroscopy;
palpation of tissue around the tumor;
checking intraocular pressure;
collection of urine and blood for analysis;
X-ray;
MRI and RCT;
biopsy.

Only after the doctor receives all the results can he prescribe medical procedures for the animal.

Treatment of melanoma

To eliminate a malignant tumor, surgery is necessary. Often, the doctor performs a V-eyelid surgery, completely removing the formation along with the growth zone. Some owners believe that only the top can be removed, but this is not true. If the tumor stalk remains in place, even more formations immediately appear on it.

If the iris is damaged, the eyeball is removed, which is then sent for histological analysis to make prognoses depending on the size, depth, and presence of metastases.

All cat and dog owners should remember that the initial stage is the least dangerous. In order not to miss the moment of its appearance, after the 5-year mark, animal owners are required to take them to an ophthalmologist veterinarian once every six months for a routine check-up. This way you will protect your pet from blindness and loss of an eye.