Radical Mastectomy for a Single Canine Mammary Tumor?

This study investigated the incidence of new tumor growth within a mammary chain after regional mastectomy. Ninety-nine intact female dogs were followed for 1 or more years after regional mastectomy that removed a single tumor in a mammary chain. Dogs with a tumor located in the cranial abdominal gland or tumors in the contralateral chain were excluded. None of the dogs were spayed at the time of mastectomy, which involved removal of the affected gland and the 2 adjacent glands. Dogs with recurrence in the contralateral chain during follow-up also had surgery, and this tumor was also evaluated. Histopathologic tumor classifications were 26% benign adenomas and 74% malignant carcinomas. Most initial tumors were in the caudal abdominal gland, followed by the inguinal gland. Dogs were more likely to develop tumors in adjacent glands than in nonadjacent glands. In addition, 87% of dogs with an initial malignancy developed an adjacent tumor, and new tumors were more likely to grow in the affected chain than in the contralateral chain. New tumor development occurred in dogs with both initial benign and malignant tumors. The authors theorized that if ovariohysterectomy had been performed at the time of surgery, tumor recurrence might have been precluded. However, published reviews on the protective qualities of spaying at the time of mastectomy have been controversial. The authors concluded that due to the high incidence of tumor recurrence in dogs with regional mastectomy, radical mastectomy (or removal of an entire chain) is the preferred method of surgical treatment for mammary tumors in dogs. This approach would preclude a second surgical intervention in affected dogs.

COMMENTARY: This study showed that tumor recurrence in a mammary chain despite complete surgical removal of the affected gland is very common in dogs. Radical mastectomy was recommended in dogs with a solitary tumor to prevent further surgeries. However, radical mastectomy in a dog is often more difficult than in a cat, due to the absence of abundant skin and subcutaneous tissue. Although this paper emphasizes a guarded prognosis for tumor recurrence if the initial lump is reported malignant, I think most would agree that removal of an entire chain at the time of the initial surgery is controversial, especially if the dog is large or of a lean breed. The information in this paper will be useful if used on an individual basis, in which prophylactic removal of an entire mammary chain may be appropriate.

Mammary tumor recurrence in bitches after regional mastectomy. Stratmann N, Failing K, Richter A, Wehrend A. VET SURG 37:82-86, 2008.