CORRESPONDENCE：In Reply

In their letter to the editor, Machens and Dralle comment on our recent article on medullary thyroid carcinoma (MTC) patients treated with radioimmunotherapy.1 They question the practicality of calcitonin doub领 time (DT) measurements as a prognostic marker. All MTC patients have calcitonin measurements before and after surgery, and some show persistent calcitonin levels after surgery, sometimes rising with time. In practice, probably because there is no established therapeutic option when surgery has failed, serial calcitonin measurements are performed before a treatment is proposed. Then, in most cases, assessing calcitonin DT with a reasonable precision is not a problem. If the DT is short (poor prognosis), a series of measurements over a couple of months may suffice; if it is long, then more time is required, but the prognosis is good in the absence of treatment.