Update on selective special types of breast neoplasms: Focusing on controversies, differential diagnosis, and molecular genetic advances

Classification of breast tumors has been evolving in the last decade. Uncommon types of breast neoplasms have been increasingly recognized. While the pathogenesis of a subset of these tumors remains to be ascertained, integration of state-of-the-art knowledge from molecular advancements and clinical practice has enhanced our understanding of these diseases, be they unique to the breast or more frequently seen in other organs. Furthermore, these lesions may have diverse clinical outcomes despite of similar histopathologic and immunophenotypic characteristics or even molecular alterations, thus warranting different clinical management. Therefore, recognizing their salient histologic features and judicious use of ancillary studies is essential to reach the correct diagnosis in the pursuit of personalized medicine. This review provides an update on selective special types of breast neoplasms, with emphasis on their salient clinicopathologic features, diagnostic pitfalls, controversies, and recent molecular genetic advances.