Mast Cell Tumors And Melanomas In Dogs

Mast Cell Tumors In Dogs

These tumors are named after mast cells, which are the cells from which they develop. Mast cells play a role in allergic responses. They are responsible for releasing histamine, (causes itching and irritation) and other chemicals. Though mast cell tumors may occur in dogs regardless of age, they are most prevalent in 8 to 10 year old dogs. The most frequent tumor sites are the chest, lower abdomen, and limbs (particularly the back of the upper thigh); though they are able to form on inner organs and other body parts. Tumors that have formed on the lower body or next to mucous membranes are more prone to spreading than mast cell tumors in other areas. Most dog breeds tend to be susceptible to the disease, in particular Boston Terriers, Boxers, Rhodesian Ridgebacks, and Pugs (exhibit multiple tumors).

Dogs can develop signs linked to the discharge of toxins from the malignant mast cells. For instance, up to 25% of dogs with mast cell tumors also have stomach ulcers as a result of histamine release. Such tumors vary significantly in volume and speed of development. They can imitate lipomas; consequently, visual signs alone cannot ascertain a diagnosis. Most commonly, a mast cell tumor looks like a raised lump or mass that may be spongy to hard to the touch. Mast cell tumors are difficult and complicated to deal with since they emerge as a large central tumor enclosed by a halo of lesser nests of mast cells that penetrate normal skin. Diagnosis is by microscopic assessment of biopsy samples, impression smears, or fine needle aspirations.

Treatment depends on the medical phase of the disease and the assumed spread of a single tumor. For a tiny solitary tumor restricted to the skin (Stage I), the favoured treatment is total surgical removal. Minute mast cell tumors may stay quiet and seem dormant for extended periods before spreading. Therefore, all mast cell tumors are on the whole treated as at least probable malignancies. The majority of veterinarians will remove at least 1¼ inches (3 cm) of healthy tissue surrounding all borders of these tumors to remove both the lump and any surrounding nests of tumor cells. If, during surgery, biopsy of a sample of the removed tissue indicates that the tumor extends beyond the primary boundary of the surgery, extra adjacent tissue will be removed. On the other hand, because mast cells are susceptible to radiation, radiation treatment may be successful if there is remaining tumor. In some cases, a combination of radiation treatment and hyperthermia (carefully increasing the dog’s body temperature while under anaesthesia) may be more effective than radiation alone. If the margins are not clean and radiation treatment is not elected, chemotherapy is also an effective follow-up treatment. Some dogs develop new tumors at regular intervals. When surgery is not performed for lingering disease or for small recurring tumors, injections of antihistamines and steroids into the tumor, which can be followed by freezing (cryotherapy), can be considered as an alternative.

To date, Stage II to IV mast cell tumors have no agreed-upon treatment. Alternative options include chemotherapy, surgical removal of the tumor and affected local lymph nodes (if reasonable), and radiation. A veterinary oncologist may advise your veterinarian in the treatment of such tumors.

Melanomas In Dogs

Melanomas are a dark-coloured tumor of the skin, which might be either malignant (cancerous) or benign (non-cancerous). Malignant melanomas are much more rarely diagnosed in dogs than benign melanomas. In middle-aged or elderly dogs, they frequently grow on the forelegs and head. The breeds most prone to these tumors are Golden Retrievers, Miniature and Standard Schnauzers, Vizslas, Doberman Pinschers, and Irish Setters. Their appearance takes the form of patches or spots; raised or flat masses. Though they tend to appear individually, melanomas may be numerous, particularly in the susceptible breeds. Surgical removal is the cure for benign tumors.

Older animals tend to develop malignant melanomas. The most at-risk breeds are Scottish Terriers, and Miniature and Standard Schnauzers. The nail beds, mouth, and lips are the most generally affected sites. Most malignant melanomas rarely develop on haired skin, and usually form on the scrotum and lower abdomen. Female dogs are not as affected as the male of the species.

The majority of malignant melanomas resemble raised, ulcerated, variably darkened bumps. If they appear in the mouth or on the lips, the tumors emerge as pink or dark to light gray, raised lumps. If they form in the nail bed, they materialize as toe swellings, with frequent loss of the nail and damage of the underlying bone.

Treatment consists of absolute surgical removal. On the other hand, the spreading nature of the tumor might make this tricky. If it is on the mouth, surgical removal of part of the jaw may allow for complete tumor removal and a suitable postsurgical cosmetic facade and survival. When present on a toe, amputation of the affected toe is the standard treatment. Melanomas are normally considered resistant to radiation treatment, and there is no recognized chemotherapy identified to be very successful. Characteristic survival times for dogs with malignant melanomas vary from 1 month to 3 years. A vaccine that was conditionally licensed by the US Department of Agriculture in 2007 helps shrivel the size of malignant melanomas in dogs and lengthen survival.

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