Cumulative survival for dogs with different types of mammary tumors

Prognostic information about any disease is essential for appointment of the most correct method of treatment and innovative therapeutic approaches. Information about the prognosis of the disease and identification of prognostic markers is extremely important, considering that almost half of the population of dogs is at risk of malignant tumors of the mammary glands (MG), and more than a third of them die within a few months after surgery [1].

         Prognosis of the disease depends on many factors, but benign tumors have a favorable prognosis [2]. A variety of different clinical parameters play a role in case of malignant tumors: the size of the primary tumor, its localization, growth rate, degree of tumor cells differentiation, a class of malignancy, the clinical stage of the disease, the presence of regional and distant metastases, infiltration into the surrounding tissue, etc. The most controlled parameters for breast malignant tumors are tumor size, lymph node status and clinical stage of the disease [3].

Histological type of the tumor is the important prognostic factor, which is among the six most important criteria by which we can predict not only the survival rates for female dogs, but also the further course of the disease [4, 5]. At the same time, data on survival of animals with various types of malignancies of MG are incomplete and contradictory; significance of histological types of tumors as a prognostic factor is not confirmed by multivariate analysis [5]. Some authors [6] deny the conclusion that complex carcinomas are generally less invasive than simple ones [7]. According to one source animals with papillary or tubular carcinoma have a more favorable prognosis than dogs with a solid or anaplastic [8, 9], others note that their survival rates are not related to histologic subtypes of adenocarcinoma [10].

Due to inconsistencies in the literature, the aim of this work was to establish the level of cumulative survival of dogs with different types of breast carcinomas.

Materials and methods. In this study was analyzed life expectancy of dogs that had been operated due to tumors of the mammary glands (77 dogs). Tumors were classified according to the WHO International histological classification of tumors of the mammary glands of dogs [11]. Plotting graphs of the cumulative survival was performed using the Kaplan-Meier method. Log-rank test was used to compare survival rates in the groups. Calculations were performed using a software package «Statistica 7 byStatSoft, Inc.». Critical significance level was taken to be 0,05.

Results. 100% survival of female dogs with benign tumors of the MG is observed for one year after surgery, and two thirds of animals outlive the 2-year period. At the same time, the survival of dogs with malignant tumors rapidly decreases with increasing time of observation. Log-rank test showed a statistically significant difference between the groups (P = 0.000001). These results confirm the previous ones, which found that the survival of dogs with benign tumors is three times higher than with malignant [2]. Among carcinomas complex ones are less invasive than simple and amongst the simple carcinomas – tubulo – papillary have a good prognosis; the distinction in the survival of dogs with this type of carcinoma was significantly different from that for dogs with solid or anaplastic (P = 0.0054 and 0.0091), which like special types of carcinomas have the worst prognosis, and animals with these tumors have the lowest average life expectancy. For solid and anaplastic tumors 2- and 4 -month survival rate was 62% and 33%. It should be noted that survival of dogs with carcinomas, which were localized in the benign tumor in the first postoperative year, is also relatively high, like in dogs with sarcomas and carcinosarcomas. It does not coincide with the opinion that sarcoma is prognostically less favorable than carcinoma [5].

Conclusion. Therefore, dogs with complex as well as with simple tubulo-papillary carcinomas of the mammary glands have a more favorable prognosis than animals with solid, anaplastic ones and special types of carcinomas. Considering that the new histological classification of tumors of MG in dogs, which was proposed in 2011, is widely discussed in the professional literature [12], the research of characteristics (in particular the prognosis) of more than 50 histological types of tumors of MG in dogs, (in particular more than 30 of them are malignant), remains a serious problem. In recent years there were attempts to standardize the procedures for assessing the results of research and treatment; however the solution to this problem is still in the future [13].

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Article published in Proceedings of the 1st European Conference on Agriculture. «East West» Association for Advanced Studies and Higher Education GmbH. Vienna. 2014. P. 59-64.