Background: Psychological comorbidity of breast cancer is a serious global health problem that inflicts huge economic and societal costs to patients themselves, families, as well as healthcare systems. The aim this study was to estimate the prevalence of common mental disorders (anxiety and depression) in breast cancer patients. Methods: The present study is cross sectional study that was a secondary analysis of a Randomized Controlled Trial in Pakistan. A total of 402 breast cancer patients were recruited from both public and private hospitals in Karachi Pakistan. Patients were assessed for depression using the structured questionnaire “Patient Health Questionnaire (PHQ-9)” and anxiety using the “Generalized Anxiety Disorder scale (GAD-7)”. Findings: Participants’ mean age was 38.9 years, majority had no formal education (77.4%). Their mean duration of breast cancer illness was 28.9 months. A large percentage of the study sample was found to be anxious (59.7%), depressed (69.4%) and had suicidal ideation (47.5%). Conclusion: High prevalence of anxiety, depression and suicidal ideation in breast cancer patients highlights the vital role of carrying out regular psychosocial assessments and offering the necessary, culturally relevant support to these patients.