Plateau phase in multiple myeloma: an end-point of conventional-dose chemotherapy

In multiple myeloma (MM) patients treated with conventional chemotherapy, the attainment and duration of a plateau phase seems to affect survival more than the degree of response to initial treatment. The aims of this study are: 1) to analyze within a cohort of previously untreated MM patients the incidence and the duration of the plateau phase; 2) to correlate it with the presenting features; 3) to assess its impact on survival.

A series of 146 consecutive MM patients treated with conventional chemotherapy were evaluated for this study. Of 146 patients, 102 responded (13 achieving complete response, 21 partial response, and 68 minimal response), and 44 showed less than minimal response or a progression. A plateau phase was documented in 115 patients (comprising all responders and 13 non responders. The median plateau phase duration was 21.6 months. The majority of patients received intermittent cycles of chemotherapy (melphalan or interferon) during the plateau phase. In multivariate analysis, lytic lesions, response, and time to the best response (TBR) correlated with the attainment of a plateau, while stage, response as a whole, and TBR showed a significant correlation with the duration. In contrast, the type of response did not correlate with either the attainment or the duration of plateau. To analyze the prognostic impact of presenting features, response to therapy and plateau we used a hierarchical model for survival. The analysis showed that the response to therapy and the duration of plateau significantly affect the survival.

In multiple myeloma a plateau phase of at least 6 months' duration has a higher impact on survival than the degree of response to conventional chemotherapy so plateau duration could be used as target of therapeutic trials. The best way to maintain the plateau phase remains, however, undefined.