During repeated Sm-153-EDTMP therapy a temporary decrease in peripheral platelet count is balanced by an increased platelet function per cell

Objectives Haematologic toxicity is a major concern after Sm-153-EDTMP therapy, in particular as repeated administration has been shown to achieve benefits beyond bone pain palliation. Recent data also indicate an additional benefit of chemo- and/or radiotherapy. We aimed to study peripheral platelet count (PPC) and total platelet function vs. functional capacity per platelet.

Methods We examined 178 patients (51 - 76 years) with hormone refractory prostate cancer with more than 1 bone lesion and/or bone pain undergoing repeated (5 times) therapy with 1,1 GBq Sm-153-EDTMP each in 3 months intervals according to the Vienna protocol. Blood was drawn before each therapy as well as in regular intervals in between for PPC and parameters of thromboxane (TX-) synthesis (TXB2 in serum, plasma, 11-dehydro-TXB2, malondialdehyde and ADP-induced platelet aggregation). Data were separately analyzed as to those patients being naïve to chemo- and/or radiotherapy or not.

Results PPC shows a significant (p<0,01) temporary decrease (nadir between 26 and 30 days at 69,6 - 78,6% of prevalue), the recovery being almost complete before the next therapy (3 months). Even after repeated Sm-153-EDTMP administration (up to 5 times) recovery of TXB2 parameters and PPC is complete. Platelet function parameters after therapy remain unchanged. If calculated per cell, however, platelet activity significantly rises, showing its peak at the PPC nadir. The response was not significantly different in those patients having received chemo- (n=19) or radiotherapy (n=31) or both (n=28) vs. naïve patients (n=100). Under careful surveillance repeated therapy with 1,1 GBq Sm-153-EDTMP is remarkably safe. During first year of Vienna protocol a decrease in PPC apparently is counterbalanced by an increased functional activity per platelet.

Conclusions Functional capacity per cell rather than PPC might therefore be the clinical determinant if Sm-153-EDTMP therapy is frequently repeated