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Tamoxifen is an important targeted endocrine therapy in breast cancer. However, side effects and early discontinuation of tamoxifen remains a barrier for obtaining the improved outcome benefits of long-term tamoxifen treatment. Biomarkers predictive of tamoxifen side effects remain unidentified. The objective of this prospective population-based study was to investigate the value of tamoxifen metabolite concentrations as biomarkers for side effects. A second objective was to assess the validity of discontinuation rates obtained through pharmacy records with the use of tamoxifen drug monitoring. Longitudinal serum samples, patient-reported outcome measures and pharmacy records from 220 breast cancer patients were obtained over a 6-year period. Serum concentrations of tamoxifen metabolites were measured by LC–MS/MS. Associations between metabolite concentrations and side effects were analyzed by logistic regression and cross table analyses. To determine the validity of pharmacy records we compared longitudinal tamoxifen concentrations to discontinuation rates obtained through the Norwegian Prescription database (NorPD). Multivariable Cox regression models were performed to identify predictors of discontinuation. At the 2nd year of follow-up, a significant association between vaginal dryness and high concentrations of tamoxifen, Z-4′-OHtam and tam-NoX was identified. NorPD showed a tamoxifen-discontinuation rate of 17.9% at 5 years and drug monitoring demonstrated similar rates. Nausea, vaginal dryness and chemotherapy-naive status were significant risk factors for tamoxifen discontinuation. This real-world data study suggests that measurements of tamoxifen metabolite concentrations may be predictive of vaginal dryness in breast cancer patients and verifies NorPD as a reliable source of adherence data.

The aim of this study was to investigate quality of life and applicability of the 10-item short form of the Nepean Dyspepsia Index (SF-NDI) in patients with subjective food hypersensitivity. Fifty-two adult patients and 120 controls were examined using three questionnaires: Quality of life Nepean Dyspepsia Index (NDI), Gastrointestinal Symptom Rating Scale (GSRS), and Ulcer Esophagitis Subjective Symptoms Scale (UESS). To document psychometric properties, 20 of the patients filled in the SF-NDI questionnaire once more 4 weeks later. Patients had poor quality of life compared with controls from health care workers or general population (P < 0.001). Scores on SF-NDI were significantly correlated with scores on the GSRS (r = 0.34, P = 0.02) and UESS (r = 0.41, P = 0.003). The SF-NDI performed very satisfactorily, with a high reliability, construct validity, and responsiveness. Patients with subjective food hypersensitivity have considerably reduced quality of life. The SF-NDI provides reliable, responsive, and clinically valid measures of quality of life in these patients.