Canine mammary tumours: Size matters–a progression from low to highly malignant subtypes

Abstract

The purpose of this study was to evaluate a possible association between mammary tumour size and increasing degree of malignancy. Data of 625 dogs with a total of 1459 mammary tumours were analysed retrospectively. 80.3% dogs were intact, mean age at diagnosis was 9.7 ± 2.5 years, 75.8% were pure breed dogs. Median body weight was 20.0 kg. Malignant tumours (n = 580) were significantly larger than their benign counterparts (1.94 cm vs 0.90 cm in mean, respectively; P ≤ .0001), resulting in a positive correlation between increasing tumour size and a change from benign to malignant (P ≤ .0001; r s = 0.214). When malignant tumours were grouped into four degrees of increasing malignancy (complex/simple/solid/anaplastic carcinomas) a significant positive correlation between increasing tumour size and more malignant tumour degree (P ≤ .0001; r s = 0.195) could be demonstrated. In a number of cases, highly malignant tumours were found to arise within less malignant lesions, supporting the concept of a further progression within the malignant tumour subtypes. In patients with multiple tumours, mean tumour sizes for malignant tumours were significantly smaller compared to patients with only one tumour (1.67 vs 2.71 cm in mean, respectively; P < .0001). These findings suggest that mammary tumours progress not only from benign to malignant but also from low to highly malignant. An increase in diameter of only a few millimetres may therefore have a big impact on the patient's outcome.

A retrospective study and survival analysis on bitches with mammary tumours spayed at the same time of mastectomy

“…Age is a risk factor for neoplastic disease in general 33 , and the median age of occurrence of CMTs ranges from 8 to 10 years [18][19][20] , in accordance with our results, that also agree on the fact that median age of bitches with benign tumors is lower than age of animals with malignant ones 21 .…”

“…The effect on time free of disease of OHE at the same time of mastectomy was evaluated in a mixed population of bitches affected by mammary tumors at different stages. The population included in the present study shared some common characteristics to those included in previous studies in terms of age, breed, spaying status, and mean size of benign and malignant tumors [18][19][20][21]25 and additional factors such as location and number of tumors were assessed. The typical presentation for the diagnosis of canine mammary tumor is middle-aged non-spayed purebred bitches, however younger and mixed breed animals can be affected.…”

“…Some history data, such as the reproductive condition, and some clinically assessable factors, such as age, tumor size and tumor number, have been described for risk of CMTs development and for their value in predicting malignancy. CMTs are typically diagnosed in older animals and the median age of occurrence ranges from 8 to 10 years [18][19][20] . A correlation exists between tumor size and malignancy, with larger masses having higher risk of malignancy 18,21 .…”

“…CMTs are typically diagnosed in older animals and the median age of occurrence ranges from 8 to 10 years [18][19][20] . A correlation exists between tumor size and malignancy, with larger masses having higher risk of malignancy 18,21 . On the contrary, the presence of multiple tumors does not necessarily indicate a high degree of malignancy or a bad prognosis, because each neoplasm can belong to a different subtype 21,22 .…”

“…[18][19][20] A correlation exists between tumour size and malignancy, with larger masses having higher risk of malignancy. 18,21 On the contrary, the presence of multiple tumours does not necessarily indicate a high degree of malignancy or a bad prognosis, because each neoplasm can belong to a different subtype. 21,22 This study is a retrospective investigation aiming to assess whether spaying at the time of mastectomy should be suggested to owners based on parameters collected in the contest of the clinical examination and on the analysis of disease-free survival (DFS).…”