Expression of p170 protein in multiple myeloma: a clinical study

The expression of the p170 multidrug resistance protein by bone marrow plasma cells (BMPC) was assessed at clinical presentation in 53 patients with multiple myeloma (MM) using the C219 monoclonal antibody. Twenty-two of the 53 (41 per cent) patients had variable aliquots (1-60 per cent, median = 6 per cent) of p170+ BMPC by immunocytochemistry. Five of 10 patients studied using bivariate flow cytometry had both diploid and hyperdiploid (DNA index ranged from 1.2 to 1.5) BMPC with hyperdiploid clones having significantly greater p170 expression than diploid ones. Of the 37 patients evaluated for a response, 20 (54 per cent) had responded to induction chemotherapy. The presence of p170+ BMPC was a negative indicator for achieving response. The response rate was 75 per cent for p170- and 25 per cent for p170+ cases (p < 0.01), with no difference on the basis of treatment schedule (melphalan and prednisone, 24 patients; peptichemio, vincristine and prednisone, 13 patients). No difference in response and survival duration was found between p170+ and p170- patients. In six of nine patients studied both at diagnosis and following induction chemotherapy the p170+ BMPC% increased irrespective of the type of treatment or outcome.