Quantitative reverse transcription-polymerase chain reaction of circulating thyroglobulin messenger ribonucleic acid for monitoring patients with thyroid carcinoma

Patients with thyroid cancer are monitored for disease recurrence by measur ement of serum thyroglobulin (Tg) and iodine-131 (I-131) scanning. To enhan ce sensitivity and to circumvent antibodies that interfere with Tg immunoas says, we have developed RT-PCR assays that detect circulating thyroid messe nger RNA (mRNA) transcripts. We now report results using a sensitive quanti tative Tg mRNA assay (Taqman; ABI, Foster City, CA) in comparison with immu noassay in patients previously treated for thyroid cancer. We evaluated 107 patients: 84 during T-4 therapy, 14 after T-4 withdrawal, and 9 at both ti me points. All patients had near-total thyroidectomy, and 92% received post operative I-131. Serum TSH, Tg protein, and Tg mRNA were measured. Patients were grouped based on most recent I-131 scan or pathologically confirmed d isease as having no detectable thyroid tissue (n = 33), thyroid bed uptake (n = 37), cervical/regional adenopathy (n = 21), or distant metastases (n = 16). During T-4 therapy, median (range) Tg mRNA values (pg Tg Eq/mu g thyr oid RNA) for the groups were 1.5 (0-26.8), 9.4 (0.5-90.0), 15.4 (0.2-92), a nd 12.4 (1.9-16.6), respectively Using a value of 3 pg Tg Eq/mu g thyroid R NA as cut-point, Tg mRNA was positive in 38% of patients with no uptake, 75 % with thyroid bed uptake, 84% with cervical/regional disease, and 94% with distant metastases. The median Tg mRNA value for patients with no uptake w as lower than the median values for patients with thyroid bed uptake (P = 0 .009) or with detectable thyroid tissue at any site (P = 0.010). Patients w ith negative I-131 whole body scans were also less likely to have detectabl e Tg mRNA levels than were patients with thyroid bed uptake (P < 0.001) or any detectable thyroid tissue at any location (P < 0.001). Similar differen ces between these groups were seen after T-4 withdrawal and for the 23 pati ents with circulating anti-Tg antibodies, when analyzed separately. Eight o f the nine patients studied with low and high TSH concentrations displayed greater amounts of circulating Tg mRNA after T-4 withdrawal. In three patie nts followed prospectively, the amount Tg mRNA correlated with the presence and absence of cervical metastases. In conclusion, we have demonstrated th at a quantitative Tg mRNA assay can identify thyroid cancer patients with r ecurrent or residual thyroid tissue with greater sensitivity and similar sp ecificity to Tg immunoassay during T-4 therapy. The assay was unaffected by anti-Tg antibodies, responded to TSH-stimulation, and was reduced after su rgical removal of metastases. These data suggest that this quantitative Tg mRNA assay may be a sensitive marker of tumor recurrence or response to the rapy, particularly in patients with anti-Tg antibodies.