Malignant mammary tumors: Biologic behavior, prognostic factors, and therapeutic approach in cats - Veterinary Medicine
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Malignant mammary tumors: Biologic behavior, prognostic factors, and therapeutic approach in cats
Most mammary tumors in cats are malignant, and metastasis is common. The prognosis depends on how far the cancer has spread and the tumor's biologic behavior, among other things. Find out how to improve the outcome in these critically ill cats.


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Table 2 Staging of Feline Mammary Tumors*
Clinical staging with a modified TNM (tumor, nodes, metastasis) staging system (Table 2) can help you determine the prognosis and help guide your treatment decisions. Perform a complete blood count, serum chemistry profile, urinalysis, three-view thoracic radiographic examination, abdominal ultrasonographic examination, and cytologic examination of regional lymph node aspirates.

TREATMENT

A combination of surgery and chemotherapy is standard for treating malignant mammary tumors in cats, but palliative care, such as with radiation therapy or analgesics, is also important.

Surgery


Figure 5. An 8-year-old female Siamese cat recovering from the second surgery of a staged bilateral mastectomy performed 10 days earlier.
Bilateral or unilateral radical mastectomy (as indicated based on lymphatic drainage) is the recommended surgical treatment for feline mammary carcinoma. Bilateral mastectomy often requires two separate staged surgeries to allow for adequate closure and healing of each surgical site (Figure 5). Radical surgical intervention results in an increased disease-free interval (575 to 1,300 days) compared with more conservative surgical approaches (300 to 325 days).4,39

Although surgery is often beneficial for controlling local and regional disease, given the aggressive metastatic behavior of feline mammary carcinomas, surgery alone should not be considered curative. In fact, surgery alone achieves only a one-year survival rate of 47% to 50% and two-year survival rate of 32% in cats.9,23,40,41 Local tumor recurrence at the surgery site or regional metastasis has been reported to occur at a median of 5.5 months in 51% to 66% of cats undergoing surgical resection of mammary carcinomas.15,19

Less aggressive palliative surgery may be considered in patients with advanced disease.

Chemotherapy

The results of several studies suggest that systemic adjuvant chemotherapy may be useful for treating mammary carcinoma after surgical excision as well as for providing pain relief in cats with nonresectable tumors. However, most clinical studies to date have been limited by their retrospective nature, small sample size, patient selection bias, variability in treatment protocols, and stage of disease treated. These confounding factors prevent discernment in treatment efficacy among various chemotherapy regimens.

Doxorubicin-based protocols are most common. In one study, single-agent doxorubicin improved the median survival time in cats with more advanced disease (stage III) compared with historical controls.42 Similarly, another retrospective study evaluating surgery and adjuvant doxorubicin reported a disease-free interval and median survival time of 255 and 448 days, respectively.43

Combining doxorubicin with cyclophosphamide has also been evaluated in both adjuvant and palliative settings. For this combination, the reported response rate for nonresectable or metastatic disease is 35% to 50%, with complete remission in 21% of patients.44,45 In addition, cats that responded to combined doxorubicin and cyclophosphamide therapy had a longer median survival time (150 to 180 days) than did those patients unresponsive to therapy (75 to 86 days).44,45 Despite the apparent efficacy of combination doxorubicin and cyclophosphamide, this treatment protocol can cause transient gastrointestinal side effects and other adverse complications, including azotemia, cardiac abnormalities, leukopenia, and anemia.44,45


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