This is a retrospective cohort study with a sample size of about 400 MM patients treated ever with at least one full cycle of bortezomib in the institution. All the patients enrolled need to be adults (≧20 years ) with measurable M-component in either blood or urine. The investigators will perform a retrospective chart review to collect clinical data, including anti-MM and concomitant medications, to evaluate the incidence and severity of BiPN in this cohort, as well as any meaningful risk factors contributed to BiPN. The investigators also plan to perform genotyping for the possible genetic factors associated with development of BiPN.