AbstractBackgroundDisease stage at diagnosis and molecular subtypes are the main determinants of breast cancer treatment strategies and prognosis. We aimed at examining the disparities and factors associated with the stage at diagnosis among the molecular subtypes in breast cancer patients in China.MethodsWe identified patients with first primary breast cancer diagnosed between January 1, 2016, and December 31, 2017, from 23 hospitals in 12 provinces in China. We analyzed the proportion of non‐early‐stage (stages II–IV) breast cancer cases based on the family history of breast cancer, body mass index (BMI), insurance status, and molecular subtypes. Multivariable analyses were used to estimate the factors associated with non‐early‐stage diagnosis among the molecular subtypes. We further compared these estimates with that in the United States using the Surveillance, Epidemiology, and End Results database.ResultsA total of 9398 Chinese were identified with first primary invasive breast cancer. Of the 8767 patients with known stages, the human epidermal growth factor receptor 2 (HER2)‐enriched subtype had the highest proportion of stages II–IV (76.6%) patients, followed by triple‐negative breast cancer (73.2%), luminal B (69.9%), and luminal A (62.3%). The percentage of non‐early‐stage patients was higher in women with overweight or obesity than in those with a body mass index (BMI) <25 kg/m2(adjusted odds ratio [OR] 1.3, 95% confidence interval (CI) 1.1–1.4). Patients with a family history of breast cancer had a higher likelihood of early‐stage (adjusted OR 0.7, 0.5–0.8) breast cancer. Patients with rural insurance had a substantially higher risk of non‐early‐stage disease than those with urban insurance (adjusted OR 1.8, 1.4–2.2). Regarding the subtype, being overweight/obese only increased the risk of non‐early‐stage in luminal A breast cancer. Compared with the United States, China had a higher proportion of non‐early‐stage breast cancer for all subtypes, with the largest gap in luminal A (adjusted OR 2.2, 95% CI 2.0–2.4).ConclusionThe wide disparities in stage at breast cancer diagnosis imply that China urgently needs to improve early breast cancer diagnosis and health equity.