Comparson og two methods for evaluation of tumor mass in multiple myeloma
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Background: The size of malignant tumours are in many instances proven or thought to mirror the risk of progression and/or death. In multiple myeloma, tumour cell mass can not be directly measured as the cells do not adhere to each other and are not in a single location. Instead, plasma cell number in bone marrow is used as a surrogate. The aim of this study was to compare, and evaluate prognostic value of two measurements of multiple myeloma cell number: The percentage of plasma cells on smear or biopsy and the number of CD138 positive plasma cells per ml bone marrow. Method: The data were extracted from the Norwegian biobank for multiple myeloma. Spearman rank correlation method was used to evaluate the correlation between the two methods, whilst Cox survival analyses were used to evaluate their prognostic value. Results: Spearman’s r=0.457, significant at the 0.01 level (2-tailed test). Cox survival analyses on progress free survival and overall survival with or without correction for ISS score and cytogenetic abnormalities gave and Exp(B) = 1.000 to 1.001 for CD138 positive cell count and 0.980 to 1.027 for percentage of plasma cells on bone marrow smear. Conclusion: The two multiple myeloma cell count methods are weakly correlated and neither give information on risk of progression or death.