A longitudinal population-based cohort study of 428,568 newly diagnosed type 2 diabetes mellitus (T2DM) patients in Shanghai, China, found that individuals diagnosed with T2DM at a younger age had a higher incidence of cancer compared to the general population. The risk of cancer was significantly higher in those diagnosed at ages 20–54 and 55–59, while those diagnosed at 75 years or older had a lower risk. The study highlights the importance of stratifying cancer risk management for T2DM patients based on their age at diagnosis. Overall cancer incidence was higher in T2DM patients than in the general population, with the highest risk observed in those diagnosed at a younger age. The risk of specific cancers, including pancreas, bladder, thyroid, kidney, breast, colorectal, and liver cancers, was also higher in younger T2DM patients. The study also found that BMI was a significant factor in cancer risk, with higher BMI levels associated with increased cancer incidence. The findings suggest that managing T2DM in younger patients requires tailored approaches to reduce cancer risk. The study underscores the need for targeted screening and prevention strategies for T2DM patients diagnosed at younger ages.A longitudinal population-based cohort study of 428,568 newly diagnosed type 2 diabetes mellitus (T2DM) patients in Shanghai, China, found that individuals diagnosed with T2DM at a younger age had a higher incidence of cancer compared to the general population. The risk of cancer was significantly higher in those diagnosed at ages 20–54 and 55–59, while those diagnosed at 75 years or older had a lower risk. The study highlights the importance of stratifying cancer risk management for T2DM patients based on their age at diagnosis. Overall cancer incidence was higher in T2DM patients than in the general population, with the highest risk observed in those diagnosed at a younger age. The risk of specific cancers, including pancreas, bladder, thyroid, kidney, breast, colorectal, and liver cancers, was also higher in younger T2DM patients. The study also found that BMI was a significant factor in cancer risk, with higher BMI levels associated with increased cancer incidence. The findings suggest that managing T2DM in younger patients requires tailored approaches to reduce cancer risk. The study underscores the need for targeted screening and prevention strategies for T2DM patients diagnosed at younger ages.