HER2 Support Group Forums - Is it ok to take antihistamines whiilst on Tamoxifen

Not really related (and I don't know the answer to your question, sorry). But although there's limited information (for example there's no info about what hormonal therapy the women were taking, nor about HER2) -- I thought this abstract from an ASCO poster was interesting. The results differed across various 2nd generation antihistamines (and some results were not significant). They say the mechanism is not known, but the abstract appears in the immunology category, and action on cytokines is mentioned.

Abstract:
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.

2015 ASCO Annual Meeting
Abstract No:3062
Citation:
J Clin Oncol 33, 2015 (suppl; abstr 3062)
Author(s): Hakan Lars Olsson, Rickard Einefors, Per Broberg; Department of Oncology, Lund, Sweden; Department of Cancer Epidemiology, Lund University, Lund, Sweden; Department of Cancer Epidemiology, Lund University, Lund, Lund, Sweden