How Many Lymph Nodes Are Enough: Assessing the Adequacy of the Number of Lymph Nodes Examined for Papillary Thyroid Cancer

Presentation Number: OR22-2
Date of Presentation: April 2nd, 2016

Timothy J Robinson*1, Samantha Thomas2, Michaela Dinan3, Randall Scheri4, Sanziana A Roman5, Julie Ann Sosa6 and Terry Hhyslop3
1Duke University Medical Center, NC, 2Duke University, 3Duke Cancer Institute, NC, 4Duke University Medical Center, 5Duke University Medical Center, Durham, NC, 6Duke University, Durham, NC


INTRODUCTION: Patients with limited numbers of lymph nodes examined are thought to be at higher risk of harboring occult disease.  However, there is a paucity of data quantifying the risk of occult nodal disease, or how many lymph nodes need to be examined to determine the true status of lymph node metastases.  

HYPOTHESIS: We hypothesized that, consistent with current clinical intuition, patients with limited lymph node examination would be at higher risk for occult nodal disease.  We further hypothesized that other adverse risk factors, such as multifocal disease, may impact overall survival.

METHODS: Data from the National Cancer Data Base (1998-2012) were used to characterize the distribution of nodal positivity of adult patients diagnosed with non-metastatic papillary thyroid cancers >1 cm with ≥ 1 lymph nodes examined.  A beta-binomial model was used to estimate the probability of occult nodal disease as a function of the total number of lymph nodes examined. This probability was then used to estimate the negative predictive value of examined lymph nodes , stratified by primary tumor characteristics, including T stage, multifocal disease, and patient age <45 years, and its association with survival.

RESULTS: 78,838 patients met study criteria, including examination of ≥1 lymph node(s).  38,738 patients (49.1%) were observed to have node positive disease. The probability of falsely identifying a patient as node-negative was estimated at 53% (1 node examined), 33% (2 examined), 24% (3), 18% (4), 14% (5), 11% (6), and <10% after examination of >6 lymph nodes.  The observed percent of patients with ≥1 positive lymph nodes varied by stage T1b-T4 (36.9% -78.6%) and was substantially higher after accounting for false negatives (47.1% - 98.4%).  In order to rule out occult nodal disease with 90% confidence, a total of 6, 9, and 18 nodes would need to be examined for patients with T1b, T2, and T3 disease, respectively.

CONCLUSIONS: Our study provides the first empirically-based estimates of occult nodal disease in patients with papillary thyroid cancer based on the primary tumor and number of lymph nodes examined. This may serve as a guideline for adequacy of lymphadenectomy examination for surgeons and pathologists in the treatment of papillary thyroid cancer.


Disclosure: JAS: member of the Data Monitoring Committee of the Medullary Thyroid Cancer Registry, funded by Astra Zeneca, NovoNordisk, GlaxoSmithKline, and Eli Lilly., Member of the Data Monitoring Committee of the Medullary Thyroid Cancer Registry. Nothing to Disclose: TJR, ST, MD, RS, SAR, TH