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BACKGROUND The American Joint Committee on Cancer (AJCC) staging system is the reference standard for describing the extent of neoplastic disease on the basis of the size of primary tumor (T), and the presence of regional lymph node (N) involvement and distant metastasis (M). Multiple foci of invasive breast carcinoma may pose staging challenges to the reporting pathologist. We set out to evaluate the practice of local breast pathologists with regard to staging of multiple foci of invasive carcinoma. PATIENTS AND METHODS Breast pathologists were surveyed at a Community of Interest in Breast Pathology meeting. The live voting survey contained 6 case-based scenarios of multiple foci of invasive mammary carcinoma of the same or different histologic type and with unilateral or bilateral involvement. A supporting illustration was provided for each case. RESULTS There was poor interobserver agreement with no consensus reached among the respondents in any of the cases. Staging choices varied from staging tumors together irrespective of histology or procedure type to staging tumors of the same histologic type together, or staging each tumor focus separately. Confusion was particularly evident when tumor foci with different histologic types were present. CONCLUSION Inconsistencies exist in the reporting of AJCC pathologic TNM stage for multiple foci of invasive carcinoma. The results serve as a reminder that education and strict adherence to the AJCC guidelines is essential for establishing standard practice in order to provide accurate cancer staging and ensure optimal clinical management.