Histogenesis
We believe that not only the rarity of PBOS but also not having enough evidence and consensus about its histogenesis have led to the lack of agreement among the management. Therefore, here we will review some of the literature in detail in order to talk about the histogenesis and the origin of the PBOS. In 2000, Hellmen et al conducted an animal study on dogs and showed that mammary spindle cell tumors and osteosarcomas are derived from pluripotent stem cells (16). In this regard, some authors believe PBOS is originated from totipotential stem cells in the mammary gland (2, 16) as it can happen after radiation to the chest wall without any significant previous lesion of trauma (9,10). In a different circumstance, there are other studies that mentioned the origin of these specific types of breast sarcoma can be the result of metaplasia, either metaplastic transformation in a pre-existing malignant lesion or non-malignant ones (17,18,19,20). Meanwhile, there are some papers that emphasized the type of pre-existing lesion such as an epithelial cancerous lesion (1,21), an intraductal papilloma (22), previous existing of a fibroadenoma(2,23), or more frequently, phyllodes tumor has been introduced as the pre-existing lesion(24,25,26,27,28,29,30). Diversely, there is a comprehensive investigation that has been published in 2012 by Emad A. Rakha that showed almost all PBOS are derived from the epithelial origin after being under the metaplastic transformation (1).