Finding and treating oral melanoma, squamous cell carcinoma, and fibrosarcoma in dogs - Veterinary Medicine
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Finding and treating oral melanoma, squamous cell carcinoma, and fibrosarcoma in dogs
The three malignancies most likely to occur in dogs' mouths can have devastating local or metastatic effects if not identified and treated quickly. Review how surgery—in conjunction with radiation, chemotherapy, or vaccination—may increase your patients' survival times.


VETERINARY MEDICINE


Advanced imaging

Advanced imaging such as CT or magnetic resonance imaging can be performed to best evaluate the extent of tumor burden and bony involvement, with CT providing better information about bone structures. These modalities are especially useful in planning surgical resection or radiation therapy.33 They can also be of benefit in evaluating retropharyngeal lymph nodes, which are difficult to assess by physical examination alone. As discussed earlier, CT may also be used to more closely evaluate the lungs for metastatic disease.

TREATMENT AND PROGNOSIS

While some oral tumors may be treated with a single modality such as surgery, many oral tumors require a combination of treatments that can include surgery, radiation therapy, chemotherapy, and immunotherapy. Treatment options vary based on the type, location, and tumor stage.

Surgery

Surgery is often the first treatment of choice (see the sidebar titled "Prognostic factors and complications associated with surgery").

Melanoma. Surgical removal of an oral melanoma is a primary method of treatment, if possible. However, surgical removal alone is not adequate for treating oral melanoma since most dogs will die of metastatic disease. Dogs treated surgically for tumors that are small (< 2 cm) and without evidence of metastasis live the longest, with a median survival time (MST) of 17 months, compared with 5.5 months in dogs with tumors that are > 2 cm or have lymph node metastasis.36,37

Because of the high percentage of cases with bone involvement, complete tumor excision requires en bloc resection of the tumor and the associated bony structures. Conservative surgery is generally not recommended because of recurrence rates > 70% and a poor MST of three to four months.3,38 However, even with complete local excision, death due to distant metastasis will still occur in most patients.

For example, radical surgeries including mandibulectomies and maxillectomies provide a lower recurrence rate compared with conservative excisions, but MSTs are similar, with most patients succumbing to metastasis.3,11,13,16,36 In three studies evaluating 59 dogs with melanoma treated with mandibular resections, the surgical procedures were well-tolerated.13,16,39 However, the MST of dogs in two of the studies was only eight to 9.9 months, with a mean survival of four months in the third study. Most of these dogs died of metastatic disease.13,16,39

Similar to partial mandibulectomies, hemimaxillectomies for oral melanoma reported in two studies evaluating 37 dogs showed a MST of 7.5 to 9.1 months.11,20 Local tumor recurrence occurred in 21% to 48% of the dogs, so even aggressive excisions may not provide clean margins for maxillary masses. At least half of the dogs' deaths were due to local progression, supporting effective local control as a means to extend survival times.20

A third study evaluating 10 dogs with oral melanoma that were treated with either mandibulectomy (four dogs) or maxillectomy (six dogs) found that local recurrence occurred in only 20% of dogs; however, the survival rate at one year was 0%.22 The results of these studies on mandibulectomies and maxillectomies in dogs with oral melanoma emphasize the importance of adjunctive treatment modalities to control both local disease and distant metastasis to provide a longer survival time.

Squamous cell carcinoma. As a primary treatment modality for mandibular or maxillary squamous cell carcinoma, surgery is associated with a longer MST than for melanoma.

Mandibular or maxillary—In 24 dogs with squamous cell carcinoma treated with partial mandibulectomies, the median disease-free interval was 26 months, with a one-year survival rate of 91%.16 Two additional studies evaluating 16 dogs with stage II or III squamous cell carcinoma treated with mandibulectomies reported a MST of seven to nine months.13,39 These MSTs may be lower because of patients with more advanced disease and a lack of censoring of patients that died of other causes, as only seven of 16 (44%) died of neoplastic disease.


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Source: VETERINARY MEDICINE,
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