Introduction: Breast cancer is the most common cancer in Iran. Delay in DIAGNOSIS is one of the causes of increased mortality in these patients. There are several obstacles to achieving an early DIAGNOSIS. This study seeks to identify the social determinants influencing breast cancer DIAGNOSIS. Methods: This qualitative study was conducted at Reza Oncology Clinic in Mashhad in 2019-2020. The study sample included 21 patients with breast cancer selected via purposive sampling. Data were collected using semi-structured in-depth interviews. Data were recorded, handwritten, and coded, subthemes were identified, and then the original themes were refined. By integrating the subthemes, they became the main themes. Findings: Economic status, life crises, social support, stigma, family history of cancer, fateful beliefs, preventive behavior, disease recognition, role conflicts, gender inequalities, and access to medical opportunities were the social factors mentioned in the narratives. Conclusion: This study has shown that social, cultural, and economic factors influence breast cancer DIAGNOSIS. Therefore, any effort to improve disease DIAGNOSIS requires a multidisciplinary approach that addresses biomedical, social, cultural, and economic factors simultaneously.