The growth and spread of many tumors are triggered by changes in cell membrane metabolism, which can lead to systemic alterations in levels of phospholipids. We sought to determine whether plasma levels of several phospholipids could differentiate between healthy remnants of thyroid tissue and residual tumor tissue or metastases in patients with thyroid carcinoma.

We measured plasma phospholipid levels by phosphorus-31 magnetic resonance spectroscopy (³¹P-MRS) in blood samples from 30 patients with thyroid cancer who had been rendered hypothyroid in preparation for diagnostic or therapeutic administration of iodine-131. All patients had undergone total thyroidectomy. Iodine-131 whole-body scintigraphy and measurements of thyroglobulin values during up to 3 years of follow-up were used to distinguish patients in remis-sion from those with only healthy thyroid remnants and those with tumor tissue or metastases.

Mean (± SD) levels of sphingomyelin (0.33 ± 0.06 mmol/L vs. 0.46 ± 0.03 mmol/L, P <0.0001) and phosphatidylcholine (1.34 ± 0.19 mmol/L vs. 2.15 ± 0.33 mmol/L, P <0.0001) were significantly lower in patients with metastatic thyroid cancer (n = 8) than in patients (n = 12) who were in remission. Patients with only remnants of thyroid tissue (n = 10) also had significantly lower phospholipid levels than did patients in remission, but significantly greater levels that did patients with tumor tissue or metastases.

These preliminary results suggest that ³¹P-MRS may be useful in helping to differentiate the presence of tumor tissue, remnants of thyroid tissue not requiring further treatment, and remission in patients with thyroid cancer.