Endocrine Abstracts

Background: Papillary thyroid microcarcinoma (microPTC), defined as PTC measuring 10 mm or less in greatest diameter, is the most common type of thyroid cancer. MicroPTC generally has an indolent clinical course, with slow and exclusivelly intrathyroidal growth, without any significant impact on patient morbidity and mortality of patients. Sometimes, even microPTC can show lymph nodes (LNs) involvement, ranging from incidental histological findings to preoperative evidence of palpable or ultrasonographic lymphadenopaties. In this specific setting, the real impact of LN metastases on the patients response to therapy is not clear.

Objectives: To determine the difference in clinicopathological features and outcomes between patients with microPTC and LNs metastases (N1) and patients with larger (> 10 mm) PTC associated with LNs or distant metastases (N1/M1).

Methods: We performed a retrospective observational study on patients diagnosed with PTC in follow-up at the Endocrinology Unit of our Institution. Clinical data of 364 patients were retrived, selecting only those who underwent total thyroidectomy, followed or not by radioiodine (RAI) therapy, belonging to one of these groups: patients with microPTC N1, patients with microPTC without histological evidence of involved LNs (microPTC N0) and patients with large PTC N1/M1.

Results: The study population included 239 patients, with no significant differences of age and sex among the three groups (Table). Among all cases of microPTC (n =155), LNs involvement was observed in 25.8% and was significantly associated with primary tumor size, extrathyroidal extension (ETE) and angioinvasion. MicroPTC N1 (n =40) was mainly diagnosed by fine needle aspiration on suspected LNs metastases respect to large PTC N1/M1 (n =84; 32.5% vs. 11.9%, P=0.006) but did not show any differences in term of histological subtypes, multifocality, angionvasion and number of involved LNs. ETE of the primary tumor was more frequent in large PTC N1/M1 than microPTC N1 group (46.4 vs. 25%, P=0.02) but lateral cervical LNs was observed more in the latter (50% vs. 31%, P=0.04). Patients with microPTC N1 were more likely to have biochemical or structural incomplete response to therapy compared with microPTC N0 (25% vs. 0, P<0.001) but as likely as large PTC N1/M1 patients (25% vs. 23.8%, P=ns). Between the two metastatic groups, patients were similar regarding the use of RAI therapy, median cumulative RAI exposure and median lenght of follow-up.

Conclusions: LNs metastases from microPTC are not uncommon and can lead to an overall treatment and a probability of disease persistence comparable to that of large PTC N1/M1.