In one study, dogs that were intact at the time of surgery for a mammary carcinoma survived a shorter time (median survival
9.5 months) than dogs ovariectomized within the two years before surgery (median survival 25 months). Dogs ovariectomized
more than two years before mammary tumor surgery did not benefit to the same extent.
In addition, dogs that were intact had a higher proportion of solid and anaplastic carcinomas than either group of ovariectomized
dogs (80 percent solid carcinomas in intact dogs, compared to 20 percent [<two years] and 7 percent [>two years]).
In another study, dogs that were not intact at the time of diagnosis were 2.5 times more likely to survive two years after
surgical excision of the mammary malignancy. In contrast, ovariohysterectomy at the time of tumor removal had no effect on
survival in another study, with approximately 60 percent of dogs with malignant tumors dying within two years of surgery whether
they were spayed at the time or not.
Duration of tumor presence
Dogs with a mammary malignancy longer than six months were more likely to develop metastases than those with tumors removed
soon after diagnosis.
Extent of surgery
The extent of surgery influences neither survival nor disease-free interval. Instead, the histopathologic completeness of
surgical margins as assessed by histopathologic examination has been shown to be prognostic for survival, so the best surgery
to achieve complete margins is the surgery that should be offered.
Effect of type of surgery on outcome for dogs with mammary tumors
Dogs with large, invasive or metastatic mammary tumors may benefit from systemic chemotherapy. Appropriate clinical studies
are essential to document the efficacy of chemotherapy, but have not yet been reported.
There are indications of activity for different chemotherapy agents from in vitro studies but there is a huge leap from these
studies to clinical efficacy. Drugs shown to have in vitro activity or potential clinical efficacy include 5-fluorouracil,
cyclophosphamide, doxorubicin, carboplatin, mitoxantrone, paclitaxel and docetaxel.
The finding that normal mammary tissue has no evidence of cyclo-oxygenase-2 (cox-2) expression, and that 24 percent of benign
and 56 percent of malignant mammary tumors do express cox-2 had led to speculation that non-steroidal inhibitors of cox-2
may play a role in the treatment of mammary carcinoma and possibly the prevention of new lesions.
In two other studies, mammary carcinomas that were more anaplastic had higher levels of cox-2 expression. In an early evaluation
of piroxicam (a non-steroidal anti-inflammatory drug) in the treatment of cancer in dogs, one of three dogs with mammary carcinoma
had a partial response to therapy.
Dr. Hoskins is owner of Docu-Tech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: