Pleomorphic adenoma of the breast: A potential morphologic and molecular pitfall in the era of genomic risk stratification

Abstract Pleomorphic adenoma of the breast is a rare, salivary-type tumor which can be misdiagnosed as invasive ductal carcinoma due to the morphologic and immunophenotypic overlap between these two entities. We report a pleomorphic adenoma of the breast initially misdiagnosed as estrogen receptor (ER)-positive low-grade invasive ductal carcinoma, a classification error which prompted genomic risk stratification with Oncotype Dx testing. This produced a high-risk recurrence score suggesting possible chemotherapeutic benefit. The patient was therefore scheduled to receive adjuvant chemotherapy following lumpectomy. However, fortunately this plan was halted when the final diagnosis of pleomorphic adenoma was rendered on the resection specimen. This is the only reported case of genomic risk stratification being performed on a salivary-type breast tumor in the literature, and it demonstrates the clinical implications of this misdiagnosis.