Implications of Body Weight Calculations for Autologous Peripheral Blood Stem Cell Transplantation.

Background: Obesity is a prevalent health problem and significant heterogeneity is seen in the body weight and BMI among adult patients undergoing autologous stem cell transplantation (SCT). At least two critical steps of the SCT are influenced by the body weight. Stem cell collection targets are usually determined based on the actual body weight and conditioning chemotherapy doses are usually determined based on corrected ideal body weight. One could hypothesize that since the stem cells home to bone marrow, the ideal body weight (IBW) being based on the height may be a better indicator of the stem cell numbers required rather than the actual body weight (ABW). Since chemotherapy doses are calculated based on corrected ideal body weight, and the volume of distribution is higher in obese patients, these patients may have decreased drug exposure and hence a higher risk of progression.

Methods: We retrospectively evaluated the engraftment kinetics and response outcome of 306 SCTs done at our institution between March 1998 and October 2001. These included patients who had undergone SCT for multiple myeloma (46%), NHL (34%), HD (6%) and AL amyloidosis (14%). Body weight, height, stem cell dose and engraftment data was obtained from medical records. The stem cell dose received was calculated based on their ABW as well as IBW and correlated with the time to white cell and platelet engraftment. We also evaluated the effect of BMI on the progression free survival after the stem cell transplant using various cut offs.

Results: The mean (range) for the ABW, IBW and BMI were 46.6 kg to 189 Kg; 45.5 kg to 94 kg; and 17.5 to 55.8 respectively. Using logistic regression, we estimated the ability of CD34 cell dose by actual and ideal body weight to predict the likelihood of platelet engraftment (50,000) by day 21 post transplant. The coefficients using both the doses were very similar (.391 for ideal and 0.361 for actual). Using Receiver operating characteristic analysis (ROC analysis); we determined the stem cell dose cutoff that best predicted for failure to engraft neutrophils by 21 days post transplantation, median CD34 dose by ABW of 3.6 million/Kg and by IBW of 4.2 million/Kg. Similarly, for failure to engraft platelets by day 30 the cutoffs were 2.89 million/Kg by actual weight and 3.77 million/kg by ideal weight. Among the individuals with actual body weight more than 25% of ideal body weight (n=122, 40%), we calculated the optimal total CD34 dose required and compared to the actual dose infused using both the cutoff sets (286 million vs. 446 million, P < 0.001 using ANC cutoff and 251 million vs. 446 million using the platelet cutoff, P < 0.001). We then examined the effect of BMI on progression free and overall survival from transplant. The progression free and overall survival post transplant was similar for patients with BMI over 30 kg/m² compared to those below this cutoff. There was no difference when patients with myeloma or lymphoma were studied separately.

Conclusion: This study, as in previous studies, confirms that stem cell dose determined on the basis of ideal body weight is comparable to that by actual body weight in terms of engraftment kinetics. In patients significantly above the ideal body weight, it is reasonable to use a target based on ideal body weight which will allow for collection of less numbers of CD34 cells, thus conserving resources. Among patient undergoing stem cell transplant, the practice of using corrected ideal body weight does not appear to compromise the outcome of stem cell transplant.