The present invention relates to methods and kits for diagnosing myeloma, monitoring disease progression or treatment efficacy in an individual having a myeloma. In one aspect, the invention relates to A method for monitoring the response of an individual to treatment for multiple myeloma, the method comprising providing cell-free nucleic acids derived from a sample of peripheral blood from an individual that has undergone treatment for multiple myeloma; assessing the cell-free nucleic acids for a mutation in any one or more nucleotide sequences from a KRAS, NRAS, BRAF and/or TP53 gene; wherein an absence of, or reduction in the number of, mutations in a nucleotide sequence from a KRAS, NRAS, BRAF and/or TP53 gene indicates a response of the individual to treatment for multiple myeloma.