Even though there was a limitation in the study that pargyline may inhibit growth of MRMT-1 cells in bone marrow of cancer pain rats and decrease tumor-secreted factors, it is still reasonable to believe that LSD1 in cancer cells metastasized into bone marrow contributed to the production of endogenous formaldehyde and cancer pain behavior in bone cancer pain rats. The gene discussed is KDM1A; the disease is bone cancer.