Seasonal purchase of antihistamines and ovarian cancer risk in the Cancer Loyalty Card Study (CLOCS): results from an observational case-control study

Objective: Antihistamine use has previously been associated with a reduction in incidence of ovarian cancer, particularly in premenopausal women. Herein, we investigate antihistamine exposure in relation to ovarian cancer risk using a novel data resource by examining purchase histories from retailer loyalty card data. Study Design: A subset of participants from the Cancer Loyalty Card Study (CLOCS) for which purchase histories were available were analysed in this study. Cases (n=153) were women in the UK with a first diagnosis of ovarian cancer between Jan 2018 to Jan 2022. Controls (n=120) were women in the UK without a diagnosis of ovarian cancer. Up to 6 years of purchase history was retrieved from two participating high street retailers from 2014 to 2022. Main outcome measures: Logistic regression was used to estimate the odds ratio (OR) and 95% confidence intervals (CIs) for ovarian cancer associated with antihistamine purchases, ever versus never, adjusting for age and oral contraceptive use. The association was stratified by season of purchase, age over and under 50 years, ovarian cancer histology, and family history. Results: Ever purchasing antihistamines was not significantly associated with ovarian cancer overall in this small study (OR:0.68, 95% CI: 0.39,1.19). However, antihistamine purchases were significantly associated with reduced ovarian cancer risk when purchased only in spring and/or summer (OR: 0.37, 95% CI: 0.17,0.82) compared with purchasing all year (OR: 0.99, 95% CI: 0.51,1.92). In the stratified analysis, the association was strongest in non-serous ovarian cancer (OR: 0.41, 95% CI:0.18,0.93). Conclusions: Antihistamine purchase is associated with reduced ovarian cancer risk when purchased seasonally in spring and summer. However, larger studies and more research is required to understand the mechanisms of reduced ovarian cancer risk related to seasonal purchases of antihistamines and allergies. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by Cancer Research UK Early Detection and Diagnosis Project (grant C38463/A26726) with additional support from the Cancer Research UK Imperial Centre, National Institute for Health Research Imperial Biomedical Research Centre, and Ovarian Cancer Action Research Centre. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The CLOCS project was reviewed and approved by the North West-Greater Manchester South Research Ethics Committee (19/NW/0427). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Access to all Cancer Loyalty Card Study (CLOCS) purchase history data collected from the retailers is restricted due to the data sharing agreements in place and the sensitive nature of the data.