RESUMO
Prolactin (PRL) acts stimulating the mammary glands development, and its deregulation has been associated to the emergence of several types of tumors, including breast cancer. Breast cancer represents the most prevalent malignancy in women, and the second cause of death in several countries. This tumor can be arise due to several molecular alterations, among them PRL has been the object of increasing interest from researchers worldwide. OBJECTIVE: To assess the association between elevated levels of plasma prolactin and breast cancer development. METHODS: A total of 158 studies were found in search databases (48 from PubMed, 69 from Scopus, 88 from Cochrane, 25 from Embase and 10 retrieved from the gray literature) after removing duplicates. Of these, 104 studies were excluded after title and abstract reading, and 54 studies were then read in full, of which only 14 were selected for this review because they had evaluated the association between PRL and breast cancer. Meta-analysis was carried out using the relative risk (RR), mean and standard deviation, confidence interval (95% CI), and the total number of patients for each study. Fixed- and random-effect models were used as applicable and, for the analysis. RESULTS: The meta-analysis showed a positive association between elevated levels of PRL and breast cancer occurrence (RR 1.26; 95%CI 1.15-1.37). Additionally, the patient sub-group analyses showed a positive association between PRL and invasive breast cancer (1.42; 1.24-1.60), ER+/PR+ (1.49; 1.23-1.75), and post-menopausal status (1.29; 1.16-1.43). CONCLUSION: The results showed a positive association between plasma prolactin levels and breast cancer, especially in women with ER+/PR + tumors, of post-menopausal age and those with invasive cancer.