Plasma cell P170 expression and response to treatment in multiple myeloma

Background. Vincristine and anthracyclines are first-line agents for the treatment of multiple myeloma (MM). P170-related multidrug resistance (MDR) may influence the response to these drugs. Materials and Methods. P170 expression of bone marrow plasma cells was assayed by immunocytochemistry (alkaline phosphatase anti-alkaline phosphatase technique) with the MRK-16 monoclonal antibody. A case was considered positive if one per cent or more of plasma cells stained as strongly as positive controls. Results. Six of 17 (35%) cases in relapse and 18/72 (25%) at diagnosis were MDR positive. MDR positivity was not found in micromolecular MM and was significantly associated with the serum beta 2-microglobulin level. Response to treatments including dexamethasone, vincristine and doxorubicin, or idarubicin, or mitoxantrone was independent of MDR positivity (50% in positive cases vs. 56% in negative ones). Conclusions. The detection of P170 in bone marrow plasma cells with the currently available methodology is not Likely to predict response to treatments that include vincristine, anthracyclines or mitoxantrone. Further studies are required to evaluate the relevance of P170-related MDR to the development of MM therapy.