Is follow-up ultrasound effective for tracking the recurrence of papillary thyroid cancer -- especially in patients with undetectable serum thyroglobulin (Tg) levels? Not necessarily, according to a study published in the October issue of the Journal of Ultrasound in Medicine.
The findings indicate that eliminating follow-up ultrasound could serve patients in the long run by relieving anxiety prompted by false positives, wrote a team led by Samantha Epstein from the University of Virginia. Previous research has shown that using follow-up ultrasound exams to monitor thyroid cancer recurrence can lead to false-positive results in up to 67% of patients.
"[An] important aspect of patient care to consider is anxiety related to false-positive results from neck ultrasound examinations performed when the serum Tg is undetectable," Epstein and colleagues noted.
Papillary thyroid cancer is the most common cancer of the thyroid gland. The standard of care for patients with lesions larger than 4 cm or metastatic disease is surgical removal, the group wrote.
After surgery, patients often undergo radioactive iodine-131 (RAI) ablation therapy, which destroys any residual thyroid tissue; they then have repeat neck ultrasound exams and Tg blood tests to monitor for cancer recurrence, usually six to 12 months after the ablation therapy and thereafter at six- to 12-month intervals. Up to 20% of patients with thyroid cancer have recurrences (J Ultrasound Med, October 2018, Vol. 37:10, pp. 2325-2331).
Epstein and colleagues sought to assess whether neck ultrasound identified recurrent disease in 76 patients with undetectable serum Tg levels after total thyroidectomy and RAI ablation for thyroid cancer. They used pathologic results from ultrasound-guided fine-needle aspiration or follow-up for at least a year as the reference standard for recurrence.
The patients collectively had a total of 257 neck ultrasound exams between April 2010 and April 2017. This included 19 exams in 18 patients in which ultrasound indicated the possibility of disease recurrence. However, none of these 18 patients actually had recurrent disease as measured by fine-needle aspiration or one-year follow-up.
The researchers also assessed 65 patients with elevated serum Tg levels, indicating the possibility of disease recurrence. They performed 24 ultrasound exams on 22 patients; 12 of these patients underwent fine-needle aspiration, and nine of them had results indicating cancer. Seven patients had follow-up ultrasound scans that did not change the initial findings, and three were lost to follow-up.
Because the diagnostic yield of neck ultrasound for thyroid cancer recurrence was significantly lower in patients with undetectable serum Tg levels than in those with elevated levels (p = 0.001), the researchers concluded that ultrasound isn't necessary.
"The results of this retrospective study support the elimination of neck ultrasound as part of routine surveillance of patients with [papillary thyroid cancer] and an undetectable serum Tg level. ... Nearly all (91.2%) neck ultrasound examinations in this subgroup yielded negative findings for abnormalities, and although 19 examinations raised the possibility of recurrence, no recurrences were identified by fine-needle aspiration or follow-up of at least one year," they wrote.
