Seasonal Variation in Skin Cancer Presentation in Primary Care Clinic in Parramatta, NSW

BACKGROUND: Seasonal variation in melanoma and keratinocyte cancer (KC) diagnoses has been noted in the literature, predominantly from northern hemisphere populations, with summer peaks most commonly noted. There is limited contemporary literature from Australian data. This is the first study to our knowledge to examine both melanoma and KC presentations in Australia, and the first to investigate this in a primary care setting. METHODS: A retrospective study was performed based on histopathological data taken from a primary care clinic in Parramatta NSW between March 2016 and March 2025. Inclusion criteria were basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma. Multiple complementary analytical approaches were performed, including cosinor harmonic regression, negative binomial models, mixed-effects models, time series decomposition, and Bayesian inference. Multiple sensitivity analyses were also performed to assess the robustness of the findings. RESULTS: 9778 skin cancers were included over a nine-year period, which included BCC; (n = 5290; 54.1%), SCC; (n = 4041; 41.3%), and melanoma (n = 447; 4.6%). Seasonal differences were statistically significant; however, clinically negligible. Conversely, there was a demonstrated reduction in presentations at the onset of COVID-19, with sustained reduction in presentations through to 2024. DISCUSSION: No clinically significant seasonal variation in skin cancer presentations was found, in direct contrast with literature from the northern hemisphere. This may reflect Australia's milder climate and relatively high annual ultraviolet index, effective public health messaging, and the accessibility of primary care services. Deficits in presentations throughout the year appear operation-dependent as opposed to biological seasonality. The significant and sustained impact of COVID-19 on skin cancer presentation raises concerns regarding the ongoing impact of delayed diagnoses of skin cancer in the Australian population. CONCLUSION: No clinically significant seasonal variation in skin cancer presentation was found in a large primary care skin cancer cohort in metropolitan Sydney; however, COVID-19 exerts a substantial and sustained impact. Vigilance regarding the long-term consequences of pandemic-related healthcare disruptions is warranted.