Cross-sectional study of seasonal patterns and implications of cancer diagnosis across calendar months

Timely diagnosis of and treatment for cancer are critical for optimizing survival outcomes. Studies suggest that seasonal calendar-related events, including holidays and vacation seasons, are associated with reduced health care delivery and accessibility. A cross-sectional study using NPCR-SEER datasets (2001-2021) characterized monthly variation in the proportion of cancer diagnoses, stage at diagnosis, and net survival across the calendar year in the USA. The authors identified 30 184 124 new cancer cases between 2001 and 2019. The highest numver of diagnoses occurred in January (8.81%), followed by June (8.60%) and October (8.58%), while the lowest number occurred in December (7.76%). These patterns persisted across individual cancer sites, clustering around the same monthly peaks and troughs. The proportion of distant-stage diagnoses was highest in January and lowest in October. The five-year survival rates ranged from worst in December (64.70%; 95% CI 64.60-64.90) to best in October (66.10%; 66.00-66.30). These patterns remained stable across the study period since 2001. The authors conclude that this cross-sectional study provides foundational evidence of consistent monthly variation in cancer diagnosis across the US.