Current research supports the role of the growth hormone/insulin-like growth factor-I (GH/IGF-I) axis in mammalian mammary tumor pathogenesis. This study assessed the prognostic value of serum and intratumoral GH and IGF-1 concentrations in mammary tumors. A total of 32 female dogs with mammary tumors and 10 healthy female dogs were evaluated in the study. Mammary glands, axillary/inguinal lymph nodes, and distant metastasis were evaluated by cytology and radiology. Tumor and lymph node excision were performed when indicated, and animals underwent tumor staging. Dogs were classified into 3 categories: healthy control, benign tumor, and malignant tumor. Hormonal concentrations were determined on fasted blood samples. Histopathologic analysis was performed on all tumors, and estrogen receptor (ER) and progesterone receptor (PR) status were assessed by immunohistochemistry. GH and IGF-1 concentrations were determined in serum and tissue homogenates. Dogs with at least 1 malignant mammary tumor underwent follow-up every 3 to 4 months, and both disease-free and overall survival times were determined. Dogs with both benign (n = 11) and at least 1 malignant (n = 21) tumors were represented in this population. All normal mammary glands were ER and PR positive. A percentage of benign tumors were ER positive (40%) and PR positive (88.8%); malignant tumors were also ER positive (10.5%) and PR positive (75%). Serum GH concentrations were significantly higher in dogs with benign and malignant tumors compared with healthy dogs. Similarly, serum IGF-1 concentrations were significantly lower in healthy dogs compared with dogs with malignant tumors. GH levels in malignant tumors were significantly higher than in benign tumors and in normal mammary glands. Tissue GH concentrations were not significantly different between benign tumors and normal mammary glands. IGF-I levels were higher in malignant tumors than in benign tumors and healthy mammary glands.

Commentary: This study demonstrates a significant relationship between canine mammary malignancies and increased levels of GH and IGF-I both in serum and tumoral tissue. These proteins were not found to be independent prognostic factors and tumor type, grade, size, and stage will continue to be our primary prognostic factors. However, novel drugs that function to block GH/IGF-I or their actions could play a role in the adjuvant therapy of dogs with malignant mammary tumors.—Erin Romansik, DVM, MS, Diplomate ACVIM (Oncology)

Serum and intratumoural GH and IGF-I concentrations: Prognostic factors in the outcome of canine mammary cancer. Queiroga FL, Perez-Alenza D, Silvan G, et al. RES VET SCI 89:396-403, 2010.