Introduction: Papillary thyroid microcarcinomas (PTMC) are defined as cancers less than 1 cm diameter in size. Most of them are indolent low-risk tumors, but some of them behave more aggressively. Therefore, there is controversy about the best postoperative surveillance of PTMC patients.
This study tested the hypothesis that PTMC patient with low mortality/recurrence risks could be identified using clinical criteria. The authors also tried to define the optimum strategy for PTMC management and long-term surveillance.
Methods: This was a retrospective analysis. The authors analyzed the data from 312 consecutively diagnosed PTMC patients with T1N0M0 stage disease. These patients did not have a history of thyroid cancer in their family, nor did they have a history of head and neck irradiation. They had unifocal PTMC, no extracapsular involvement, and classic papillary histotypes. Another inclusion criterion for these patients was complete follow-up data from surgery to at least 5 years after diagnosis.
These 312 patients had undergone total thyroidectomy. Additionally, 137 (44%) were treated with radioactive iodine ablation (RAI) of the thyroid remnant following surgery (RAI group). All patients were monitored yearly with assays (serum thyroglobulin, TSH, thyroglobulin antibody) and cervical ultrasonography (US).
Results: PTMC was diagnosed by fine-needle aspiration biopsy in 25% of patients before surgery, but represented an incidental finding after thyroidectomy for goiters in the remaining 75%. Median follow-up was 6.7 years (range, 5 to 23 years). During follow-up, there were no deaths caused by thyroid cancer and there were no reoperations. The first post-operative US exams, performed 6 to 12 months after surgery, and the last US exams during follow-up were all negative, showing no evidence of lymph node involvement.
In the RAI group, final serum thyroglobulin levels were undetectable (<1 ng/ml). In the non-RAI group, final serum thyroglobulin levels were undetectable in 93% of patients. Twelve patients had detectable Tg levels (1.3-6.0 ng/ml), and in all 12 this level had remained stable or decreased during follow-up. The patient with the highest Tg level had no evidence of diseases by ultrasound or 131-I whole body scan.
Conclusion: Accurate risk stratification can allow for a safe follow-up of most PTMC patients with a less intensive, more cost-effective protocol. Cervical ultrasonography is essential in that protocol. A negative finding at the first postoperative exam is highly predictive of a favorable long-term outcome.
Commentary by Kresimira (Mira) Milas MD
Papillary thyroid microcarcinoma has now become the most commonly diagnosed thyroid malignancy in patients older than 45 years (Hughes et al, Thyroid 2011; 21 (3):231-6) but the optimal management of these cancers has been a matter of debate. The article summarized above comes from the large Papillary Thyroid Cancer Study Group that accrues information from 9 hospital-based referral centers for thyroid disease in Italy. It demonstrated the excellent long-term outcomes for patients with PTMC who met the following criteria: no family history of thyroid cancer, no history of head and neck irradiation, T1N0M0 staging, no tumor extension beyond the thyroid capsule, unifocality, no aggressive histologic subtypes (eg. tall cell),and no local/angioinvasion. About 75% of all PTMC patients will meet these criteria.
Defining an optimal surveillance pattern is necessary so that the projected larger population of patients with this diagnosis receive appropriate care, and particularly, that they are not over-treated. To this end, the authors contribute yet another publication that advocates risk-stratification, a concept that has become emphasized in recent years for all types of differentiated thyroid cancer. It is worthwhile to become familiar with other literature on this topic (Tuttle et al, Thyroid 2010 Dec;20(12):1341-9; Oncology 2009 Jun;23(7):592, 600, 603; Endocr Pract 2008 Sep;14(6):764-74; Endocrinol Metab Clin North Am 2008 Jun;37(2):419-35).
The cohort of patients described by Durante et al would be defined as “very-low” risk for recurrence and death from thyroid cancer. The above criteria define patients who are most likely to experience complete cure with total thyroidectomy, and who can avoid postoperative 131-I ablation and TSH suppression. Yearly ultrasound examinations were consistently negative, thus suggesting that in this subgroup of patients, annual US is probably unnecessary, especially after the first 5 years of follow-up. Annual neck physical examination and thyroglobulin measurement may constitute a more cost-effective protocol. Ideally, these findings would be confirmed in a randomized prospective study, but they offer a basis for a thoughtful management approach in the new era of PTMC.