Editor: We read with great interest the excellent review on diagnostic imaging in multiple myeloma by Dr Angtuaco and colleagues in the April 2004 issue of Radiology (1). We would like to address just a few issues related to the use of technetium 99m (Tc) sestamibi. In the past few years, different groups have reported consistent results by using this tracer in patients with multiple myeloma (2–7). In particular, several investigators (4–6) evaluated successfully the use of Tc sestamibi in the follow-up of these patients. For instance, we found that all patients that had negative findings with Tc sestamibi imaging at follow-up were actually in remission (either complete or partial), while 86% of those that had positive findings experienced disease progression (4). In their review article, Dr Angtuaco and colleagues (1) pointed out the limited value of Tc sestamibi in the follow-up evaluation due to the development of the multidrug resistant phenotype, which causes a decrease of net tracer accumulation. We agree that the enhanced outward transport of the tracer in Pgp-overexpressing tumors actually decreases the net cellular uptake of Tc sestamibi. It should be noted, however, that this effect is time dependent and particularly evident at 2–4 hours postinjection (8,9). Therefore, by using an appropriate acquisition time (ie, 10 minutes after tracer injection), tracer uptake is not affected markedly by multidrug resistance. Furthermore, the washout rate of the tracer can be estimated and may be used to assess multidrug resistance in multiple myeloma, as reported for other types of tumors (9–11). Finally, we recently reported (12,13) the dependence of tracer influx from Bcl-2 overexpression and showed that malignant tumors with absolute lack of tracer uptake on early images have a defective apoptotic program and high levels of Bcl-2. These observations may have important clinical implications for patients with multiple myeloma.