(1) Background: Metastasis is a complex process in which the primary cancer cells spread to a distant organ or organs, creating a secondary tumour location, which in many patients leads to treatment failure and death. The aim of the present study was to assess the association of endothelial markers (i.e., sP-selectin, sE-selectin and von Willebrand factor) with the leptin-to-adiponectin ratio (LAR) and to perform an analysis of the predictive value on the survival of patients with luminal A and B invasive breast cancer (IBrC). (2) Methods: The trial included 70 previously untreated women with a median age of 54.5 years and a median tumour size of 1.5 cm. The concentrations of pre- and post-treatment endothelial markers, leptin, and adiponectin were evaluated with specific ELISA kits. The median duration of follow-up was 68.5 months (interquartile range (IQR) = 59–72 months) with a recurrence rate of 15.71%. (3) Results: Regardless of the treatment pattern, endothelial marker concentrations and the LAR increased after treatment. The follow-up showed a significantly higher relapse rate in patients with IBrC who had higher pre-treatment sP-selectin and post-treatment LAR levels. A post-treatment LAR of 0.83 ng/mL with a sensitivity of 88.9% and specificity of 57.9% was established as the optimal cut-off value for distinguishing patients with or without disease recurrence. Additionally, a higher risk of breast cancer relapse was associated with a lower post-treatment sP-selectin concentration. (4) Conclusions: Our results showed mainly that pre-treatment sP-selectin levels and post-treatment LAR may have a value as prognostic indicators and may contribute to predicting the future outcome in patients with early-stage IBrC.