TO THE EDITOR:
The report by Helal et al. (1) provides convincing evidence of the superiority of 18F-FDG PET for localization of residual thyroid carcinoma in a small patient cohort presenting with a difficult problem in the management of this disease. However, their conclusions about therapeutic and patient outcome efficacy raise some questions (2). Although PET was said to have initiated surgery for removal of a residual tumor in 23 patients, implicitly 5 of these had had some abnormality on conventional imaging (Tables 1 and 2 in (1)). It would have been helpful if the authors had gone into more detail on the process whereby PET was decisive, especially as this bears on the significance of the disease-free status achieved by 14 patients. Might not additional cervical lymph nodes, for example, have been identified in a conventionally initiated surgical exploration? Assuming, however, that without PET 14 more patients would have continued with occult residual disease, the real question is of the net benefit achieved by the extra interventions for the group as a whole. From an oncologist’s perspective, this benefit needs to be expressed in terms of patients’ length and quality of life and ideally offset against the expenditure involved. A figure of $50,000 per quality-adjusted life-year is often quoted, and some analysis of this nature is required to support conclusions about “undeniable clinical value” of imaging technologies (3). We hope Helal et al. will take this next step in putting numeric flesh on the sense of improved patient outcome that their report provides.
REPLY:
18F-FDG PET in differentiated thyroid carcinoma concerns only a few patients with metastases that do not concentrate 131I, and the benefit of 18F-FDG PET expressed in terms of “patients’ length and quality of life and ideally offset against the expenditure involved” is difficult to determine without undertaking a multicenter study involving large groups of patients. Differentiated thyroid carcinoma represents less than 1% of all cases of cancer and has, above all, a generally good prognosis: 80%–95% survival to 10 y (1).
However, it is important to underline 2 points. First, most patients with thyroid carcinoma are cured from the first treatment and are then followed up with long-term monitoring, based on the relatively low cost of the thyroglobulin assay. However, recurrence will develop in 5%–20%, and their long-term prognosis will then depend on how soon the recurrence is detected and treated (2). Furthermore, recurrent disease that does not concentrate radioactive iodine has a negative outcome, and so it is important to detect recurrence by whatever means, as soon as possible, allowing a treatment other than 131I.
The second point to underline is that in our group of 37 patients who could have been expected to have a negative outcome, 18F-FDG PET detected recurrence in 19 of the 27 patients who had a negative morphologic assessment, leading to a cure in 10 patients and to a change in treatment in 4 others. Of the other 10 patients, 18F-FDG PET made it possible to stick to the proposed surgery for 5, whereas a change of treatment was envisaged for the other 5.
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