Metastatic lymph node size, extension predict PTC recurrence risk

LAKE BUENA VISTA, Fla. — The presence of lateral lymph node metastasis and extrathyroidal extension identified patients with papillary thyroid carcinoma with an intermediate or high risk for recurrence, according to study results presented at the International Thyroid Congress.

These factors can be used to decide if patients are appropriate candidates for radioiodine (RAI) ablation, according to the researchers.

“We attempted to perform a risk stratification based on lymph node metastasis,” Hyung Suk Kim, MD, of the department of surgery at The Catholic University of Korea, said during a presentation. “We believe them to be an important prognostic factor. Our study was designed to identify clinical risk factors for recurrence and to create a risk stratification.”

Regional neck lymph node metastasis serves as a known predictive factor for papillary thyroid carcinoma recurrence. However, the significance of metastatic lymph node size and ratio have rarely been studied, according to study background.

Thus, Kim and colleagues sought to identify the clinicopathologic significance of these factors.

The study included data from 580 patients (women, n = 409) with papillary thyroid carcinoma who underwent thyroidectomy with central lymph node dissection or modified radical neck dissection. Patients underwent RAI ablation following surgery.

The researchers divided patients into two groups based on metastatic lymph node size (pN1mic: 0.2 cm; pN1mac: > 0.2 cm). They then stratified patients based on metastatic lymph node size and lymph node ratio (low: pN1mic and ratio 0.4 cm; intermediate, pN1mic and ratio > 0.4 cm or pN1mac and ratio 0.4 cm; high: pN1mac and ratio > 0.4 cm).

The researchers classified the majority of patients (n = 375) as pN1mac. Factors associated with larger metastatic lymph nodes included extrathyroidal extension, tumor size and lateral lymph node metastasis (P < .001 for all).

Further, a greater number of metastatic lymph nodes (P < .001), higher T stage and N stage (P < .001 for both), and higher metastatic lymph node ratio (P = .011) significantly predicted pN1mac.

The two groups had significantly different mean stimulated thyroglobulin (sTg) levels after surgery (pN1mic = 1.29 ng/mL; pN1mac = 2.52 ng/mL; P = .03).

Further, sTg appeared to gradually increase for each risk cohort (low = 1.02 ng/Ml; intermediate = 2.14 ng/mL; high = 3.3 ng/mL; P = .004).

In a multivariate analysis, lateral lymph node metastasis, grossly extrathryoidal extension and a larger number of metastatic lymph nodes remained significantly associated with pN1mac.

The researchers determined that RAI ablation can be omitted for patients in the low-risk group.

“We have created a risk stratification model based on metastatic lymph node size and ratio,” Kim said. “Patients and clinicians should consider the potential risk for recurrence before undergoing RAI ablation.” – by Cameron Kelsall

Reference:

Hong Y, et al. Short Oral Communication 47. Presented at: International Thyroid Congress; Oct. 18-23, 2015; Lake Buena Vista, Fla.

Disclosure: The researchers report no relevant financial disclosures.