Second Generation Antihistamines after Breast Cancer Diagnosis to Improve Prognosis Both in Patients with ER+ and ER- Breast Cancer.

3062 Background: Subgroups of patients with breast cancer (BC) could be candidates for immunological interventions. In the present investigation the role of antihistamines on prognosis of breast cancer has been studied, especially comparing first and second generation H-1 receptor antagonists due to their possible different effects on cytokines. Methods: The study includes all women with BC diagnosed in Sweden 2000 through 2008 (n = 54406). Dates of birth, BC diagnosis and TNM-stage were directly extracted from the cancer registry. Therapy with antihistamines was gathered from the Swedish Prescription Registry. Other registries utilised were the Cause of Death Registry, Population Registry, and the in patient or out patient registries. BC and overall survival was compared between users of antihistamines and non users. Analyses were adjusted for TNM-stage, receptor status and age at diagnosis. A late entry model was used for different types of antihistamines. Results: The HR for BC specific survival for the combined group of antihistamine users (n = 9777) was 0.70 (0.66-0.75). All the effect was seen for use after BC diagnosis. Results remained after adjusting for out or in patient diagnoses of allergy. In late entry models women using desloratadine (n = 1895) had a HR of 0.69 (0.52-0.91). Loratadine users (n = 2132) HR of 0.74 (0.60-0.93). Cetirizine users (n = 3001) HR of 1.13 (0.96-1.33) and Klemastine users (n = 2278) had a HR of 0.98 (0.80-1.19). Ebastin users (n = 326) had a HR of 0.50 (0.22-1.12) and Fenofexadine users (n = 145) had a HR of 0.73 (0.30–1.76). The analyses was also stratified for ER-status, but the results did not differ noticeably. Results were similar when overall survival was analysed. Conclusions: This population based registry study shows that women treated with second generation antihistamines have a better overall and BC specific survival compared with non users regardless of age, history of allergy, ER status and tumor stage. The results are strongest for desloratadine use and use after BC diagnosis. Second generation antihistamines could offer a nontoxic therapy for both receptor positive and negative BC. The mechanism behind this effect is presently unknown.