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Prognostic utility of a test in cats with malignant mammary tumors

Naito E, Yuki M, Hirano T, Kainuma D, Aoyama R. Prognostic utility of preoperative neutrophil–lymphocyte ratio in cats with malignant mammary tumors. Res Vet Sci. October 2020.

Malignant mammary tumors are commonly encountered in intact female cats or those who underwent multiple heat cycles prior to spaying. Therapy of mammary cancer is based on removal of the tumor in combination with radical (and preferably bilateral) mastectomy to remove all mammary tissue, potentially in combination with chemotherapy. Despite this. Metastatic disease and tumor related death is common. Several prognostic factors have been investigated, including tumor size and the presence of metastasis, and histologic findings including lymphatic invasion and tumor characteristics. Many of these are only evaluable after surgery. Tools to determine prognosis pre-operatively would be useful to screen cases that will respond best to aggressive therapy.

The neutrophil to lymphocyte ratio (NLR) is a simple calculation attained for standard CBC results that has been shown to have prognostic utility in several human and veterinary conditions. Elevation to the NLR indicates a stress or inflammatory leukogram, with neutrophilia or lymophopenia worsening the value. This purpose of this paper was to determine if NLR has a prognostic values in cats with malignant mammary neoplasia.

The study was designed as a retrospective observational study of cats presenting to a veterinary clinic from 2008 to 2017. Laboratory tests were evaluated at first presentation, and cats underwent regional, unilateral, or bilateral mastectomy. Cats undergoing local mastectomy or with concurrent inflammatory disorders, concurrent neoplasia, or distant metastasis at diagnosis were excluded. After surgery, tumor size, lymph node and vascular invasion, and survival time were recorded.

34 cats were included in the study. All were female, and 9 were spayed with a median age of 11.8 years. Median tumor size was 1.5cm; 9 cats had single tumors while the remainder had multiple. Four cats had tumor ulceration. 5 cats underwent bilateral mastectomy, 16 unilateral, and 13 regional. All cancers were diagnosed as malignant adenocarcinoma. 11 cats received post operative chemotherapy with either doxorubicin or carboplatin.

NLR were measured pre operatively on all cats. In univariate analysis, large tumor size and elevated NLR were associated with a shorter survival time. Multivariate analysis showed only NLR as a significant predictor of outcome. ROC curves were calculated for NLR and tumor size. The AUCROC for NLR was 0.88, compared to 0.74 for tumor size. Using a cut-off of 5.67, sensitivity and specificity for one year survival were 93.8% and 88.9% respectively. No other factor was found to have a significant correlation with survival.

This study determined that the NLR can be used as a perioperative prognostic factor for cats with mammary neoplasia. Several limitations were present, including the retrospective nature, which limited the degree of analysis and study design. A small number of patients were included, and larger sample sizes may give more information. Full staging was not performed in all cats, and surgical and medical therapies were not standardized. Finally, the effects of concurrent diseases on NLR were not investigated.

Further research into the NLR in cats, including its alterations and prognostic values in varied conditions should be investigated. (MRK)

See also:

Gemignani, F., Mayhew, P.D. Association of surgical approach with complication rate, progression-free survival time, and disease-specific survival time in cats with mammary adenocarcinoma: 107 cases (1991-2014). J. Am. Vet. Med. Assoc. 2018 252, 1393–1402.