Correlation between the number of lymph node metastases and lung metastasis in papillary thyroid cancer.

CONTEXT

A prognostic classification system based on aggregate numbers of lymph node metastases may better estimate the risk of distant metastasis.

OBJECTIVE

This investigation sought to evaluate a papillary thyroid cancer (PTC) patient's risk of distant metastasis.

DESIGN

This was a retrospective analysis.

SETTING

The setting was a tertiary referral center.

PATIENTS

Included were 972 PTC patients.

INTERVENTION

The intervention was compartment-oriented surgery.

MAIN OUTCOME MEASURE

The main outcome measure was lung, bone, and liver metastasis.

RESULTS

Eighty-seven (9.0%) of the 972 PTC patients had distant metastases to lung (79 patients), bone (16 patients), liver (two patients), brain and skin (one patient each). For distant metastasis, more than 20 lymph node metastases had a specificity of 90.8% and a negative predictive value of 92.7%, whereas sensitivity and positive predictive value were low (27.6 and 22.9%). On multivariate logistic regression, 1-5, 6-10, and 11-20 involved nodes denoted a moderate risk of lung metastasis [odds ratio (OR), 9.9, 10.6, and 13.8; P ≤ 0.004], whereas more than 20 involved nodes indicated a high risk of lung metastasis (OR, 25.0; P < 0.001). Mediastinal lymph node metastasis carried a moderate risk of lung metastasis (OR, 7.5; P = 0.001). When these numeric categories of lymph node metastases were exchanged for current tumor node metastasis (TNM) N categories, the OR decreased from 25.0 (for > 20 lymph node metastases) to 16.4 (N1b), and from 9.9-13.8 (for 1-20 lymph node metastases) to 4.7 (N1a).

CONCLUSION

In PTC, categories of 0, 1-20, and more than 20 lymph node metastases correlate better with lung metastasis than current TNM N categories N0, N1a, and N1b.