Tamoxifen, a vital component in the treatment of hormone receptor-positive breast cancer, has long been recognized for its efficacy in reducing cancer recurrence and mortality.3 However, because the ocular side effects of tamoxifen, particularly tamoxifen maculopathy, present a critical concern in clinical practice for tamoxifen users, 1,2 our study investigated the risk of macular conditions potentially associated with tamoxifen toxicity among users. From a comprehensive analysis of the demographic and clinical characteristics of the tamoxifen user cohort, our findings on the factors influencing the risk of maculopathy may contribute to the growing body of knowledge concerning the risk and risk factors of maculopathy in tamoxifen users, a topic not extensively studied.
Tamoxifen retinopathy can present in several forms4–8,11−14 and similarities with macular telangiectasia, type 2 have been noted in previous studies1,15 Therefore, the macular abnormalities observed on OCT in tamoxifen users may be recognized as a different condition, rather than tamoxifen maculopathy. Furthermore, this maculopathy has not been adequately recognized by ophthalmologists due to limited awareness; thus, it is likely that it has been misdiagnosed as other macular conditions such as macular degeneration and macular edema than toxic maculopathy. To maximize capturing potential macular conditions associated with tamoxifen toxicity, we included several macular conditions for the outcomes while excluding patients with such conditions prior to tamoxifen use. This might have led to an underestimation of the incidence of tamoxifen maculopathy if the analysis was limited to the code for toxic maculopathy in our cohort, which was found to be less than 1%.
The cumulative incidence in previous studies varied from 0.9–12%, largely depending on the cumulative dose in the study population.1,8 Furthermore, macular diseases generally occur in elderly individuals, indicating the susceptibility of older patients to macular diseases. Recent studies have reported higher incidence rates than previous studies, which might be partly explained by advances in retinal imaging and its increased sensitivity in detecting microscopic retinal changes in tamoxifen users. Our study, including the patients undergoing OCT imaging, showed maculopathy excluding common macular diseases, the most specific category for tamoxifen maculopathy among our outcomes, in 11% of overall tamoxifen users. This was comparable to the recent figure of 12% among patients receiving tamoxifen.8
The cumulative incidences of overall macular diseases, other maculopathy excluding common macular diseases, and macular edema, stratified by cumulative dose and age categories, provide valuable insights into the dose-response relationship between drug exposure and maculopathy incidence and age-related susceptibility. The statistical significance of these trends further strengthens the evidence of the impact of these factors on maculopathy risk. The increasing cumulative incidence observed in older age groups and with higher cumulative tamoxifen doses highlights the relevance of age and cumulative tamoxifen dosage in the development of macular conditions. This underscores the need to simultaneously consider both factors in maculopathy screening, suggesting that future guidelines should incorporate these aspects when formulating screening recommendations.
Assessment of risk factors for macular diseases in tamoxifen users also revealed significant associations with demographic and systemic disease factors. Sex, age, diabetes mellitus, hypertension, and kidney disease are substantial contributors to the risk of maculopathy. Notably, dyslipidemia did not exhibit a significant association with macular conditions, although a recent study identified hypercholesterolemia as a risk factor for tamoxifen maculopathy.8 These findings emphasize the relationship between a few systemic diseases potentially affecting retinal diseases such as diabetes and hypertension and development of tamoxifen-induced maculopathy. The heightened vulnerability of older individuals, as indicated by the increasing HR with age, underscores the need for vigilant monitoring of this demographic subgroup. Interestingly, despite the potential impact on drug metabolism and excretion, liver diseases showed no significant association with the incidence of macular diseases. This observation is notable considering that tamoxifen is primarily excreted by the liver and biliary tract, implying that liver disease may influence the systemic concentration of tamoxifen. However, liver function could not be assessed in this study, which limits drawing conclusion on the association between liver diseases or function and tamoxifen maculopathy incidences.
While our study provides valuable insights into the risk factors and cumulative incidence of tamoxifen-induced maculopathy, certain limitations must be acknowledged to ensure a nuanced interpretation of the findings. The retrospective nature of our study, which relied on the HIRA database, introduced some inherent limitations. The identification and classification of macular conditions were based on specific KCD-8 codes within the dataset, potentially leading to misclassification or under-reporting. The operational definitions used for the inclusion and exclusion criteria may not have captured all relevant cases, thus contributing to selection bias. The absence of direct clinical assessments and the reliance on diagnostic codes may result in an incomplete representation of tamoxifen maculopathy status.
Moreover, we acknowledge the possibility of unmeasured confounding factors that were not accounted for in our analysis. Lifestyle factors, genetic predisposition, and other medications that could influence the development of maculopathy were not comprehensively considered in our study. Furthermore, the generalizability of our findings may be limited because this study focused exclusively on the South Korean population. Healthcare systems and patient demographics vary across regions, and caution should be exercised when extending our results to other populations with different characteristics.
Despite these limitations, our study provides a robust exploration of the risk factors and cumulative incidence of diverse macular conditions among tamoxifen users at the national level. The insights gained from this study have implications for clinical practice by guiding the formulation of evidence-based guidelines for tamoxifen-induced maculopathy screening. The intricate interplay between age, cumulative tamoxifen dosage, and systemic diseases highlighted in this study serves as a foundation for future research and enhances our understanding of the ocular complications associated with this widely prescribed breast cancer therapy. Future research may further address tamoxifen maculopathy in diverse ethnic groups by incorporating more detailed clinical assessments to identify tamoxifen-induced maculopathy and by considering a broader range of potential confounding factors to enhance the generalizability of our findings.