Surgical dose and the clinical outcome in the treatment of mammary gland tumours in female dogs: a literature review

Mammary gland tumours are the most frequent tumours in intact female dogs and surgery remains the main treatment modality. Surgery is traditionally performed according to the lymphatic drainage of the mammary glands, but robust evidence is still lacking on what surgical dose is the smallest and results in the best outcome. The objective of the study was to investigate whether choice of surgical dose influences treatment outcome in dogs with mammary tumours and to identify current gaps in research that need to be filled in future studies for identifying the smallest surgical dose with the best possible outcome. Articles for entrance into the study were identified in online databases. Information regarding outcome following use of different surgical doses was extracted for analysis. Also, known prognostic factors were mapped for each study to discuss their impact on treatment outcome. Twelve articles were identified and included. Surgical dose applied ranged from lumpectomy to radical mastectomy. Radical mastectomy was most often analysed [11/12 (92%) articles]. Less invasive surgical doses were used less often in decreasing order of invasiveness. Outcomes analysed were most often survival time [7/12 (58%) articles], frequency of recurrences [5/12 (50%) studies] and time to recurrence [5/12 (42%) studies)]. No studies demonstrated any significant association between surgical dose and outcome. Gaps in the research could be categorised as data that was not available for extraction, for example known prognostic factors. Other factors related to study design were also identified, for example small groups of dogs included into the study. No studies showed a clear benefit of choosing one surgical dose over the other. Choice of surgical dose should be based on known prognostic factors and risks for complications rather than on lymphatic drainage. In future studies all prognostic factors should be included when investigating how choice of surgical dose influences treatment outcome.