FOS and cancer: A possible explanation for BMD massive reduction during NAC and worse prognosis after esophagectomy is that cancer derived proinflammatory cytokines including Interleukin (IL)‐1, IL‐6, and tumor necrosis factor (TNF)‐α, may activate NF‐κβ and c‐Fos, resulting in the differentiation of osteoclast genesis in patients with cancer.