TGFβ1 is expressed by bone myeloid cells [29,30,50,51,52,53], is the predominant TGFβ isoform in bone [54,55], and is released from bone matrix stores into the bone microenvironment during osteolysis, an event that dominates in the majority of breast cancer BMETs [56], regardless of the tumor subtype. The gene discussed is TGFB1; the disease is breast carcinoma.