The circadian clock is strongly influenced by the sun exposure and prostate cancer has been shown to be inversely proportional to it. We investigated whether PCa aggressiveness in Montreal, Quebec, Canada, differs over the months during or following potentially longer exposure to sunlight. We analyzed 3447 patients treated between January 1995 and December 2023 with primary radiotherapy for localized PCa. We investigated whether the month when diagnostic biopsy was performed was associated with a more frequent diagnosis of a primary Gleason score (pGS) of 4 or 5. We grouped the months of biopsy into the four quarters (Q1–4) of the year. Multivariable logistic regression was used to predict a pGS of 4 or 5, adjusted for age and year of biopsy. There were significantly fewer biopsies (P = 0.027) with pGS 4 or 5 in the last 3 months of the year (Q4; 19.0%) than those in Q1–3 (22.9%). Age, prostate-specific antigen (PSA) level, and the number of positive biopsies were not significantly different between Q4 versus Q1–3. In multivariate logistic regression analysis, a biopsy in Q4 was significantly predictive of a lower risk of pGS 4 or 5 (odds ratio [OR]: 0.77, 95% confidence interval [CI]: 0.63–0.93, P = 0.007), as was older age (P < 0.001), but not the year of biopsy (P = 0.76). In conclusion, patients biopsied during Q4 had a 23% lower risk of a pGS 4 or 5 on diagnostic biopsy than those biopsied during the previous 9 months. Our results are not a proof of causality.

Keywords: biopsy; Gleason score; prostate cancer; sun exposure